Piezoresistive sensor for detecting a physical disturbance

ABSTRACT

A sensor includes a plurality of piezoresistive elements and a plurality of electrical connection terminals. The plurality of piezoresistive elements are fabricated on a first side of a substrate. A second side of the substrate is configured to be coupled to an object where a physical disturbance is to be detected. A plurality of electrical connection terminals are coupled to the first side of the substrate.

CROSS REFERENCE TO OTHER APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNo. 62/545,391 entitled PIEZORESISTIVE SENSOR filed Aug. 14, 2017 whichis incorporated herein by reference for all purposes.

BACKGROUND OF THE INVENTION

Piezo components can be used to detect and/or apply a physicaldisturbance (e.g., strain, force, pressure, vibration, etc.). There aretwo types of piezo components, piezoelectric and piezoresistive. Withpiezoelectric components, when a physical disturbance is applied on thecomponent, the piezoelectric component produces a voltage/charge inproportion to the magnitude of the applied physical disturbance. Thiseffect is reversible. Applying a voltage/charge on the piezoelectriccomponent produces a mechanical response proportional to the appliedvoltage/charge. Piezoelectric components are often made of crystal orceramic materials such as PZT (i.e., lead zirconate titanate). Withpiezoresistive components, when a physical disturbance is applied on thecomponent, the piezoresistive component produces a change in resistancein proportion to the magnitude of the applied physical disturbance.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the invention are disclosed in the followingdetailed description and the accompanying drawings.

FIG. 1 is a schematic diagram illustrating an embodiment of apiezoresistive bridge structure.

FIG. 2A is a diagram illustrating various views of an embodiment of anASIC packaging of a piezoresistive sensor chip.

FIG. 2B is a diagram illustrating various views of another embodiment ofa packaging of a piezoresistive sensor chip.

FIG. 3 is a flowchart illustrating an embodiment of a process forproducing a piezoresistive sensor.

FIG. 4 is a diagram illustrating an embodiment of a system for detectinga physical disturbance (e.g., strain, pressure, etc.).

FIG. 5 is a diagram illustrating an embodiment of a system that sharestransmitters and receivers among banks of bridge structures fordetecting physical disturbances (e.g., strain).

FIG. 6 is a flowchart illustrating an embodiment of a process fordetecting a signal disturbance using one or more sensors.

FIG. 7A is a block diagram illustrating an embodiment of a system fordetecting a touch input surface disturbance.

FIGS. 7B-7D show different embodiments of transmitter and sensorcomponent arrangements utilized to detect a touch input along a surfacearea (e.g., to detect touch input on a touchscreen display).

FIG. 8 is a block diagram illustrating an embodiment of a system fordetecting a touch input.

FIG. 9 is a flow chart illustrating an embodiment of a process forcalibrating and validating touch detection.

FIG. 10 is a flow chart illustrating an embodiment of a process fordetecting a user touch input.

FIG. 11 is a flow chart illustrating an embodiment of a process fordetermining a location associated with a disturbance on a surface.

FIG. 12 is a flow chart illustrating an embodiment of a process fordetermining time domain signal capturing of a disturbance caused by atouch input.

FIG. 13 is a flow chart illustrating an embodiment of a processcomparing spatial domain signals with one or more expected signals todetermine touch contact location(s) of a touch input.

FIG. 14 is a flowchart illustrating an embodiment of a process forselecting a selected hypothesis set of touch contact location(s).

FIG. 15A is a diagram illustrating different views of a device withtouch input enabled housing.

FIG. 15B is a block diagram illustrating an embodiment of a system fordetecting a touch input surface disturbance.

FIG. 15C is a diagram illustrating an embodiment of a device housingwith touch input enabled sides.

FIG. 15D shows a magnified view of the cavity/pocket.

FIG. 15E shows transmitters and receivers mounted on fingers of a flexcable.

FIGS. 15F-15H show different embodiments of transmitter and sensorcomponent arrangements utilized to detect a touch input along a lineararea.

FIG. 16 is a flowchart illustrating an embodiment of a process to detecta touch input.

FIG. 17 is a diagram illustrating an embodiment of a receiver and twoassociated transmitters in the side of a phone.

FIG. 18 is a flowchart illustrating an embodiment of a process toidentify a touch input in a part of a first region that is not part of asecond region using signal amplitudes.

FIG. 19 is a flowchart illustrating an embodiment of a process toidentify when a touch input leaves a part of a first region that is notpart of a second region using signal amplitudes.

FIG. 20 is a flowchart illustrating an embodiment of a process to usetime-shifted versions of the same PRBS when transmitting.

FIG. 21 is a diagram illustrating an embodiment of a side of a phonewith multiple transmitters and multiple receivers.

FIG. 22 is a flowchart illustrating an embodiment of a process to filtera received signal.

FIG. 23 is a diagram illustrating an embodiment of a signal afterpassing through different types of touches, if any.

FIG. 24 is a diagram illustrating two embodiments of a discrete signalconstructed using amplitude metrics.

FIG. 25 is a flowchart illustrating an embodiment of a process toidentify a touch input using a first amplitude metric associated withthe part of the first region that is not part of the second region.

FIG. 26 is a flowchart illustrating an embodiment of a process togenerate a first amplitude metric associated with a part of a firstregion that is not part of a second region.

FIG. 27 is a flowchart illustrating an embodiment of a process toidentify a touch input using a second amplitude metric associated withthe second region.

FIG. 28 is a flowchart illustrating an embodiment of a process togenerate a second amplitude metric associated with a second region.

FIG. 29 is a block diagram illustrating an embodiment of a touch andforce sensor.

DETAILED DESCRIPTION

The invention can be implemented in numerous ways, including as aprocess; an apparatus; a system; a composition of matter; a computerprogram product embodied on a computer readable storage medium; and/or aprocessor, such as a processor configured to execute instructions storedon and/or provided by a memory coupled to the processor. In thisspecification, these implementations, or any other form that theinvention may take, may be referred to as techniques. In general, theorder of the steps of disclosed processes may be altered within thescope of the invention. Unless stated otherwise, a component such as aprocessor or a memory described as being configured to perform a taskmay be implemented as a general component that is temporarily configuredto perform the task at a given time or a specific component that ismanufactured to perform the task. As used herein, the term ‘processor’refers to one or more devices, circuits, and/or processing coresconfigured to process data, such as computer program instructions.

A detailed description of one or more embodiments of the invention isprovided below along with accompanying figures that illustrate theprinciples of the invention. The invention is described in connectionwith such embodiments, but the invention is not limited to anyembodiment. The scope of the invention is limited only by the claims andthe invention encompasses numerous alternatives, modifications andequivalents. Numerous specific details are set forth in the followingdescription in order to provide a thorough understanding of theinvention. These details are provided for the purpose of example and theinvention may be practiced according to the claims without some or allof these specific details. For the purpose of clarity, technicalmaterial that is known in the technical fields related to the inventionhas not been described in detail so that the invention is notunnecessarily obscured.

As compared to piezoresistive components, piezoelectric components areoften more sensitive and thus can be used to detect smallerperturbations. However, piezoresistive components do have an advantageover piezoelectric components when performing a static measurement.Because a fixed amount of voltage/charge is generated by a piezoelectriccomponent in response to a constant applied force/pressure, when theapplied force is maintained, the piezoelectric component outputs adecreasing signal as imperfect insulating materials and reduction ininternal sensor resistance cause a constant loss of electrons. Thus itis difficult to accurately detect a static strain/force/pressure thathas been applied on a piezoelectric component for the entire timeduration of a lengthy application. On the other hand, withpiezoresistive components, the change in resistance remains constant inresponse to an applied static force/pressure and thus staticforce/pressure can be more reliably detected.

This makes piezoresistive components a better choice for use in buildinga strain gauge. However, the limited physical disturbance sensitivity ofpiezoresistive components often hinders its application. Additionally,piezoresistive components are extremely sensitive to temperature andmanufacturing variations can significantly affect accuracy andconsistency of its output.

In some embodiments, a strain sensor includes a plurality ofpiezoresistive elements fabricated on a first side of a substrate. Asecond side of the substrate is configured to be coupled to an objectwhere a strain is to be detected. A plurality of electrical connectionterminals are coupled to the first side of the substrate, allowing powerand signals to be provided/received from the strain sensor.

FIG. 1 is a schematic diagram illustrating an embodiment of apiezoresistive bridge structure. Piezoresistive bridge structure 100includes four piezoresistive elements that are connected together as twoparallel paths of two piezoresistive elements in series (e.g.,Wheatstone Bridge configuration). Each parallel path acts as a separatevoltage divider. The same supply voltage (e.g., V_(in) of FIG. 1) isapplied at both of the parallel paths and by measuring a difference involtage (e.g., V_(out) of FIG. 1) between a mid-point (e.g., between thepiezoresistive elements R₁ and R₂ in series as shown in FIG. 1) at oneof the parallel paths to a mid-point of the other parallel path (e.g.,between the piezoresistive elements R₃ and R₄ in series as shown in FIG.1), a magnitude of a physical disturbance (e.g., strain) applied on thepiezoresistive structure can be detected. However, the piezoresistiveelements are extremely sensitive to temperatures and manufacturingvariabilities. Thus precisely matched piezoresistive elements typicallymust be utilized in the piezoresistive bridge structure. However, whenseparate piezoresistive elements are mounted on a material to producethe resistive bridge structure, it can be difficult and costly to ensurethey are precisely matched and homogenous.

In some embodiments, rather than individually attaching separate alreadymanufactured piezoresistive elements together on to a backing materialto produce the piezoresistive bridge structure, the piezoresistivebridge structure is manufactured together as a single integrated circuitcomponent and included in an application-specific integrated circuit(ASIC) chip. For example, the four piezoresistive elements andappropriate connections between are fabricated on the same siliconwafer/substrate using a photolithography microfabrication process. In analternative embodiment, the piezoresistive bridge structure is builtusing a microelectromechanical systems (MEMS) process. Thepiezoresistive elements may be any mobility sensitive/dependent element(e.g., as a resistor, a transistor, etc.).

In some embodiments, the semiconductor substrate of the piezoresistiveelements is a monocrystalline substrate (e.g., as opposed to apolycrystalline substrate). Although a polycrystalline substrate iscommonly utilized in microfabrication of resistive elements of priorapproaches, in the context of one or more of the embodiments describedin this specification, the grains of the polycrystalline substrate maylead to inconsistent and undesirable behavior when the piezoresistiveelements are subjected to strain. Thus by utilizing a monocrystallinesubstrate with a more consistent crystal structure, the piezoresistiveelements behave in a more consistent and desirable manner when understrain.

In some embodiments, the micro fabricated silicon wafer/substrate haspiezoresistive elements built on one side of the wafer/substrate, andexternal connections (e.g., connections for supply voltage and sensoroutput) to the structure are made from the side with the fabricatedpiezoresistive elements. This leaves the backside of the structure/chipfor attachment to an object where the physical disturbances are to bedetected using the chip. However, the thickness of a silicon wafer usedin typical microfabrication is too thick to effectively transmitstrain/force/pressure/vibration from the back surface to the componentson the other side. In some embodiments, the backside of the siliconwafer/substrate is reduced (e.g., sanded) down to reduce the thicknessof the final chip to facilitate the physical disturbance to travelthrough the thickness of the substrate. For example, starting from anoriginal thickness of 750 microns, the substrate is sanded down to beless than 300 microns (e.g., sanded to a thickness of 100 microns) afterfabricating the piezoresistive structures. In some embodiments, in orderto facilitate external connections, preformed solder balls areformed/deposited/coupled to the substrate/chip to facilitate theexternal connections to the chip from its front/device side (i.e., sideopposite the backside of the chip where the piezoresistive elements havebeen fabricated). Using preformed precision solder balls on the chipensures manufacturing reliability. For example, when the piezoresistivebridge structure chip is attached to an object where the physicaldisturbance is to be detected, an adhesive (or tape) is applied to thebackside of the chip and a force is applied on the opposite side of thechip (e.g., force applied on side with the preformed solder balls) topress and couple the chip on the object. The chip may break or becomeattached unevenly at an angle if the solder balls are uneven or notconsistent.

FIG. 2A is a diagram illustrating various views of an embodiment of anASIC packaging of a piezoresistive sensor chip. Sensor chip 200 includesa fabricated structure of piezoresistive bridge structure 100 of FIG. 1.Chip 200 has five connection points (e.g., where the preformed solderballs have been placed) including two connections for the supply input,one for ground/bias, and two connections for sensor output (e.g., wherevoltage output indicating magnitude of physical disturbance isdetected). An adhesive may be applied to the top side (e.g., facesbackside of the semiconductor substrate) of chip 200 for coupling to anobject where physical disturbances are to be detected. Bottom of chip200 (e.g., faces component manufactured side of the semiconductorsubstrate) includes preformed precision solder balls (e.g., two forplus/minus of input, one for ground/bias, and two for plus/minus ofsensor output). Chip 200 has been configured in a manner to be rotationinvariant (e.g., for four different orientations) during installation.For example, orientation of the chip with respect to receiving contactpads (e.g., on a flexible printed circuit cable, circuit board, etc.)that attaches to the solder balls of chip 200 does not matter as long asthe receiving contact pads line up with the pattern of solder balls dueto the symmetrical nature of the pattern of solder balls (e.g.,symmetrical along multiple different axes) as well as interchangeabilitybetween the input connections and the output connections given thesymmetrical nature of the chip schematics.

FIG. 2B is a diagram illustrating various views of another embodiment ofa piezoresistive sensor chip. Sensor chip 202 includes a fabricatedstructure of piezoresistive bridge structure 100 of FIG. 1. Chip 202 hassix connection points including two connections for the supply input,two for ground/bias, and two connections for sensor output (e.g., wherevoltage output indicating magnitude of physical disturbance isdetected). An adhesive may be applied to the top side (e.g., facesbackside of the semiconductor substrate) of chip 202 for coupling to anobject where physical disturbances are to be detected. Bottom of chip202 (e.g., faces component manufactured side of the semiconductorsubstrate) includes exposed conductive surface portions corresponding tothe six connection points and can be connected corresponding connectionpads (e.g., on a flexible printed circuit, a circuit board, etc.). Ineffect, chip 202 utilizes land grid array (LGA) structures as connectionpoints for sensor chip 202.

Although an example of chip 200 of FIG. 2A utilized preformed solderballs, chip 202 does not necessarily have to utilize preformed solderballs on its connection points/pads/pins (e.g., to attach chip 202 to aflex circuit cable/board). Rather, a solder paste can be applied to theconnection points of chip 202, placed into contact with thecorresponding contact pads of the receiving circuit cable/board (e.g.,flexible printed circuit cable) and heated to perform reflow soldering.The heat will melt the solder paste and reflow the solder material tojoin together the connection points of chip 202 with the correspondingcontact pads of the circuit cable/board. However, a challenge with usingreflow soldering is achieving even heating of the connection points. Forexample, heat applied on top of chip 202 will flow around the sides ofthe chip to heat the sides before reaching the center of the chip. Ascompared to chip 200 of FIG. 2A, chip 202 does not include a connectionpoint in the middle of the chip to allow more even heating of theconnection points placed around the perimeter of the chip without aconnection in the center of the chip. Although use of reflow solderingto attach a CPU chip to a rigid circuit board has been done inelectrical manufacturing, use of reflow soldering to attach a chip to aflexible printed circuit is believed to be novel and is at least partlyenabled by the configuration and relative small size of chip 202.

In some embodiments, as compared to chip 200 of FIG. 2A, an additionalconnection point has been added to make chip 202 symmetrical androtation invariant (e.g., for two different orientations). For example,orientation of chip 202 with respect to receiving contact pads (e.g., ona flexible printed circuit cable, circuit board, etc.) that attaches toconnection points of chip 200 does not matter as long as the receivingcontact pads line up with the pattern of the chip connection points dueto the symmetrical nature of the pattern of the chip connection pointsas well as interchangeability between the input connections and theoutput connections given the symmetrical nature of the chip schematics.In some embodiments, chip 202 is not necessarily rotation invariant anda mark (e.g., circle mark shown on top view of FIG. 2B) on a top side ofchip 202 indicates an orientation of the chip (e.g., indicates thatconnection point/pad/pin number 1 is underneath near the chip cornerwhere the mark is placed).

FIG. 3 is a flowchart illustrating an embodiment of a process forproducing a piezoresistive sensor. For example, the process of FIG. 3 isutilized to at least in part manufacture sensor chip 200 of FIG. 2Aand/or 202 of FIG. 2B.

At 302, piezoresistive elements and connections between them arefabricated on a substrate. For example, piezoresistive elements andconnections between them (e.g., in a bridge structure configuration) arefabricated on the same semiconductor wafer/substrate (e.g., made ofsilicon, gallium arsenide, or other semiconductor materials) using aphotolithography microfabrication process. In alternative embodiment,the piezoresistive bridge structure is built using amicroelectromechanical systems (MEMS) process. Examples of thepiezoresistive element include a resistor, a transistor, and anymobility sensitive/dependent element.

At 304, a thickness of the substrate with the fabricated piezoresistiveelements is reduced. In some embodiments, the micro fabricated siliconwafer/substrate has piezoresistive elements fabricated on one side ofthe wafer/substrate, and external connections (e.g., connections forsupply voltage and sensor output) to the structure are made from theside with the fabricated piezoresistive elements. This leaves thebackside of the structure/chip for attachment to an object where thephysical disturbances are to be detected using the chip. However, thethickness of a silicon substrate may be too thick to effectivelytransmit strain/force/pressure/vibration from the back surface to thecomponents on the other side. In some embodiments, the backside of thesubstrate is reduced (e.g., sanded) down to reduce the thickness of thefinal chip to facilitate the physical disturbance to travel through thethickness of the substrate. For example, starting from an originalthickness of 750 microns, the substrate is sanded down to be less than300 microns (e.g., sanded to a thickness of 100 microns) afterfabricating the piezoresistive structures.

At 306, terminal connections to the piezoresistive elements are formed.

In some embodiments, in order to facilitate external connections,preformed solder balls are formed/deposited/coupled to thesubstrate/chip to facilitate the external connections to the chip fromits front/device side (i.e., side opposite the backside of the chipwhere the piezoresistive elements have been fabricated). In someembodiments, terminal connections to the piezoresistive elements areformed prior to reducing the thickness of the substrate. Using preformedprecision solder balls on the chip ensures manufacturing reliability.For example, when the piezoresistive bridge structure chip is attachedto an object where the physical disturbance is to be detected, anadhesive (or tape) is applied to the backside of the chip and a force isapplied on the opposite side of the chip with the preformed solder ballsto press and couple the chip on the object. The chip may break or becomeattached unevenly at an angle if the solder balls are uneven or notconsistent.

In some embodiments, rather than using preformed solder balls, terminalconnections to the piezoresistive elements are at least in part formedusing solder paste. For example, the solder paste can be applied to theconnection points of chip 202 of FIG. 2B, placed into contact with thecorresponding contact pads of a receiving circuit cable/board (e.g.,flexible printed circuit cable) and heated. The heat will melt thesolder paste and reflow the solder material to join together theconnection points of chip 202 with the corresponding contact pads of thecircuit cable/board.

FIG. 4 is a diagram illustrating an embodiment of a system for detectinga physical disturbance (e.g., strain, pressure, etc.).

In some embodiments, structure 100 of FIG. 1, sensor chip 200 of FIG.2A, and/or sensor chip 202 of FIG. 2B may be utilized for ultrasonicsignal sensing applications. For example, it can be used to replacepiezoelectric receivers in sensing propagated vibration signalstransmitted by piezoelectric actuators/transmitters. Given thepiezoresistive elements of the resistive bridge structure that rely onmobility modulation within the silicon substrate as it encountersultrasound waves, the resistive bridge structure can function as areceiver. Likewise, since the mobility modulation of substrate stressinto electrical signal is a physical function of silicon, it can also beused to sense absolute changes in stress and strain. In someembodiments, chip 200 includes temperature sensing and compensationcapabilities, which work with a fixed set of calibration signals beingsent from a transmitter.

However, the challenge of using the piezoresistive elements as anultrasonic signal sensor/receiver is the difficultly of using them tosense minute changes in physical disturbances caused by the ultrasonicsignal. For example, a physical disturbance desired to be detected mayonly cause a 0.001% change in resistance of the piezoresistive elements,leading to microvolt output signals that are difficult to accuratelydetect digitally given their small magnitude. With a DC voltage biasedpiezoresistive bridge structure, this level of variation is difficult todetect, especially given noise (e.g., pink noise, noise picked up fromexternal sources, etc.) affecting the sensor/receiver.

In some embodiments, rather than using a DC bias voltage, a higherfrequency signal is utilized as the bias/supply voltage of thepiezoresistive bridge structure. The output of the piezoresistive bridgestructure will output a modulated version of the input supply signal inproportion to a magnitude of physical disturbance sensed to thestructure. Signal processing can be performed on the output signal tocharacterize and quantify this magnitude.

In some embodiments, a system includes a plurality of piezoresistiveelements configured in a resistive bridge structure. A signaltransmitter is coupled to the resistive bridge structure and configuredto send an encoded signal to the resistive bridge structure. A signalreceiver is coupled to the resistive bridge structure and configured toreceive a signal from the resistive bridge structure. The receivedsignal is correlated with the sent encoded signal in determining ameasure of strain.

System 400 includes sensor bridge structure 402, signal transmitter 404,and signal receiver 406. An example of sensor bridge structure 402 isbridge structure 100 of FIG. 1. In some embodiments, sensor bridgestructure 402 is packaged as sensor chip 200 of FIG. 2A and/or sensorchip 202 of FIG. 2B that is connected to signal processor component 410that includes signal transmitter 404 and signal receiver 406.Transmitter 404 provides an input supply signal to sensor bridgestructure 402. Rather than being a constant DC voltage, signaltransmitter 404 provides the supply signal at a high frequency (e.g.,between 50 kHz and 1 MHz). By using a higher frequency signal, pinknoise (i.e., 1/f noise) can be reduced and filtered out, resulting inincreased signal detection sensitivity. In some embodiments, theprovided input supply voltage is an encoded digitally modulated signal.For example, a carrier signal (e.g., between 50 kHz and 1 MHz) ismodulated using a digital signal (e.g., a signal encoding a pseudorandombinary sequence (PRBS)).

As physical disturbance is applied to imbalance structure 402 and altersthe resistance of its piezoresistive elements, output from sensor bridgestructure 402 received by signal receiver 406 is a version of the inputsupply signal provided by signal transmitter 404 with anamplitude/intensity/gain change that is proportional to the physicaldisturbance.

Signal processor component 410 includes other components not shown inthe diagram of FIG. 4 to illustrate the embodiment more clearly. Forexample, signal processor component 410 may include a microprocessor, asignal driver, a signal generator, a controller, a DSP engine, an ADC,and/or a signal conditioner.

FIG. 5 is a diagram illustrating an embodiment of a system 500 thatshares transmitters and receivers among banks of bridge structures fordetecting physical disturbances (e.g., strain).

In some embodiments, the output from a sensor bridge structure (e.g.,piezoresistive bridge structure) is provided as a physical input to asignal receiver of a processor component that receives and processes theoutput to determine the sensed mechanical disturbance magnitude.However, as the number of sensor bridge structures that are utilizedincreases, a signal processing component requires an increasing numberof receivers given that a separate receiver component is required foreach different signal to be received in parallel. It may be difficult,inefficient, and costly in many cases to accommodate such a large numberof receivers.

In some embodiments, outputs from a plurality of sensor bridgestructures are electrically connected together such that the pluralityof sensor bridge structures share the same receiver (e.g., share thesame connection interface/wire of the receiver). This means that thesignal outputs from a plurality of sensor bridge structures will becomecombined together when the same receiver receives it. In order to beable to distinguish between signals from different piezoresistive bridgestructures, each structure of the group of structures connected togetherutilizes a different input supply signal (e.g., by a differenttransmitter). By correlating the combined output against each of thedifferent supply signals, the output corresponding to eachpiezoresistive bridge structure is able to be selectively obtained. Insome embodiments, different encoded digitally modulated signals (acarrier signal, e.g., between 50 kHz and 1 MHz, is modulated using adigital signal, e.g., PRBS signal) are utilized for differentpiezoresistive bridge structures. In some embodiments, the differentsupply signals provided to each of the piezoresistive bridge structuresare different phases (e.g., time shifted versions) of the same modulatedPRBS signal.

The increase in the number of supply signals means that the number oftransmitters has been increased as a tradeoff in reducing the number ofreceivers. However, the same supply signal is able to be shared (i.e.,sharing the same transmitter) with other bridge structures that do notshare/combine their outputs (e.g., do not share the same receiver). Insome embodiments, there exists a plurality of banks of piezoresistivebridge structures, where each bank of piezoresistive bridge structuresshares a common connection/wire to a receiver but each piezoresistivebridge structure of the bank is provided different input supply signalsfrom different transmitters. Additionally, one bridge structure fromeach bank of the plurality of banks share a common transmitter and areprovided the same input voltage source signal. In some embodiments, asingle signal processor component includes the different transmittersand receivers. Thus by sharing both transmitters and receivers, thetotal number of transmitters and receivers that are utilized is able tobe reduced. For example, without receiver sharing, a group of 32piezoresistive bridge structures will require 1 transmitter and 32receivers for a total of 33 transmitter/receiver components. Howeverwith both transmitter and receiver sharing, only 4 transmitters and 8receivers are required (e.g., 4 banks of 8 bridge structures) for atotal of 12 transmitter/receiver components.

Sensor bridge structures 502 and 504 belong to a first bank of sensorbridge structures and share receiver 512 of signal processor component510. Sensor bridge structures 506 and 508 belong to a second bank ofsensor bridge structures and share receiver 516 of signal processorcomponent 510. Sensor bridge structures 502 and 506 share transmitter514 that provides a first input supply signal, and sensor bridgestructures 504 and 508 share transmitter 518 that provides a secondinput supply signal. An example of each of sensor bridge structure 502,504, 506, and 508 is bridge structure 100 of FIG. 1. In someembodiments, each of sensor bridge structure 502, 504, 506, and 508 ispackaged as sensor chip 200 of FIG. 2A and/or sensor chip 202 of FIG.2B. Signal processor component 510 includes other components not shownin the diagram of FIG. 5 to illustrate the embodiment more clearly. Forexample, signal processor component 510 may include a microprocessor, asignal driver, a signal generator, a controller, a DSP engine, an ADC,and/or a signal conditioner.

FIG. 6 is a flowchart illustrating an embodiment of a process fordetecting a signal disturbance using one or more sensors. The process ofFIG. 6 may be performed by signal processor component 410 of FIG. 4,signal processor component 510 of FIG. 5, touch detector 720 of FIGS.7A-7D, touch detector 802 of FIG. 8, and/or touch detector 1520 of FIG.15B.

At 602, one or more input supply signals are provided to one or moresensors. For example, voltage supply signal(s) are provided to one ormore sensor bridge structures (e.g., bridge structures shown in FIGS. 4and/or 5). An example of the sensor bridge structure is a piezoresistivebridge structure produced using the process of FIG. 3. In someembodiments, each supply voltage signal is an encoded digitallymodulated signal. For example, a carrier signal (e.g., between 50 kHzand 1 MHz) is modulated using a digital signal (e.g., signal encoding apseudorandom binary sequence (PRBS)).

In some embodiments, a plurality of sensors are provided the same supplyvoltage signal. In some embodiments, there exists a plurality of sensorsand at least a portion of the sensors is provided a different supplyvoltage signal from another portion of the sensors. The different supplyvoltage signals may differ by being modulated using a different digitalsignal (e.g., encoding a different PRBS) and/or by having differentphases (e.g., time shifted versions of the same modulated PRBS signalare used as the different signals). In some embodiments, there exists aplurality of banks of bridge structures, where each bank of bridgestructures shares a common connection to a receiver but eachpiezoresistive bridge structure of the bank is provided different inputsupply signals from different transmitters. Additionally, one bridgestructure from each bank of the plurality of banks shares a commontransmitter and is provided the same input voltage source signal. Insome embodiments, a single signal processor component includes thedifferent transmitters and receivers.

At 604, one or more output signals are received from the one or moresensors. For example, as physical disturbance is applied to imbalancethe resistive bridge structure of the sensor to alter the resistance ofits resistive elements, an output signal from the sensor is a version ofthe input supply signal with an amplitude/intensity/gain change that isproportional to the physical disturbance. In some embodiments, adifferent output signal is received from each of the one or moresensors. In some embodiments, output signals from a plurality of sensorsthat share a connection to the same receiver have become combined (e.g.,super imposed) on a combined output signal received by the receiver andthe received combined output signal is to be processed to separate thedifferent output signals from the different sensors.

At 606, the one or more received output signals are filtered. Forexample, an output signal is high pass filtered, low pass filteredand/or anti-alias filtered to reject/reduce noise (e.g., filter toisolate signal portion within frequency range of the encoded digitallymodulated input signal and reject signal frequency components outsidethe range of the input signal).

At 608, each of the filtered received output signals is correlated witha corresponding input supply signal to determine a correlation result.For example, a cross-correlation is performed between a filteredreceived output signal and the corresponding input signal that wasprovided to the sensor that provided the corresponding received outputsignal. Because the input signal travels through the elements (e.g.,piezoresistive elements) of the sensor almost instantaneously, theoutput signal and the input signal are correlated from each otherwithout any delay or lag and the correlation result may indicate acorrelation value between the signals without any delay or lag from eachother. In some embodiments, a filtered combined output signal includescomponent output signals from a plurality of different sensors and thesame filtered combined output signal is correlated with each of thedifferent input supply signals of the different sensors to determine aseparate corresponding correlation result for each of the differentsensors. In some embodiments, the correlation result is a correlationresult signal. In some embodiments, the correlation result is a value.

At 610, the correlation result for each of the one or more sensors isutilized to determine a physical disturbance magnitude valuecorresponding to a disturbance detected by the corresponding sensor. Forexample, a magnitude value indicating an amount of force, pressure, orstrain detected by the sensor is determined and provided for use as theforce, pressure, or strain magnitude of a touch input. In someembodiments, the disturbance magnitude value is proportional to anamplitude value of the corresponding correlation result. For example,the amplitude value of the corresponding correlation result or a scaledversion of the amplitude value of the corresponding correlation resultis provided as the disturbance magnitude value. In some embodiments, amaximum amplitude value of the corresponding correlation result isidentified and utilized in determining the disturbance magnitude value.

In some embodiments, the determined physical disturbance magnitude valueis a calibrated value. Due to minor residual manufacturing variations,temperature variations, and other sources of errors, a sensor may detecta minor false mechanical disturbance even though no mechanical/physicaldisturbance is being applied. In some embodiments, a calibration isperformed (e.g., periodically performed) to detect and correct it. Forexample, output signal from the piezoresistive bridge structure isdetected at steady-state when no physical disturbance is being appliedand any detected physical disturbance magnitude (e.g., correlationresult amplitude value) at steady-state is determined as the calibrationoffset value/factor. This calibration offset value is subtracted from adetected physical disturbance magnitude (e.g., subtract calibrationoffset value from an amplitude value of a correlation result) todetermine a calibrated physical disturbance magnitude result that isprovided as an output force, pressure or strain magnitude value.

FIG. 7A is a block diagram illustrating an embodiment of a system fordetecting a touch input surface disturbance.

A piezo receiver device can be utilized to detect a location of a touchinput on a surface. For example, a user touch input on the glass surfaceof a display screen is determined by detecting at the piezo receiverdevice coupled to the glass, a disturbance to an ultrasonic signal thathas been transmitted and propagated through the glass. In someembodiments, a signal such as an acoustic or ultrasonic signal ispropagated freely through a propagating medium with a surface using apiezo transmitter coupled to the propagating medium. When the surface istouched, the propagated signal is disturbed (e.g., the touch causes aninterference with the propagated signal). In some embodiments, thedisturbed signal is received at a piezo sensor coupled to thepropagating medium. By processing the received signal and comparing itagainst an expected signal without the disturbance (e.g., transmittedsignal), a location on the surface associated with the touch input is atleast in part determined. For example, the disturbed signal is receivedat a plurality of sensors and a relative time difference between whenthe disturbed signal was received at different sensors is used todetermine and triangulate the location on the surface. In someembodiments, time differences associated with the plurality of resultsare used to determine a location associated with the disturbance. Insome embodiments, each of the time differences is associated with a timewhen signals used in the correlation are most correlated. In someembodiments, the time differences are associated with a determined timedelay/offset or phase difference caused on the received signal due tothe disturbance. This time delay may be calculated by comparing a timevalue determined using a correlation with a reference time value that isassociated with a scenario where a touch input has not been specified.The result of the comparison may be used to calculate a location of thedisturbance relative to the locations of sensors that received theplurality of signals. By using the location of the sensors relative to asurface of a medium that has propagated the received signal, a locationon the surface where the disturbance to the propagated signal originatedmay be determined.

In some embodiments, the piezo transmitter is a piezoelectrictransmitter. In various embodiments, the piezo sensor/receiver includesa piezoelectric sensor and/or a piezoresistive sensor (e.g.,piezoresistive bridge structure). Because piezoelectric sensors aretypically more sensitive than piezoresistive sensors as previouslydescribed, piezoelectric sensors are better suited for use in detectingpropagated ultrasonic signals in many applications. However, becausepiezoresistive sensors are also able to more reliably detect constantstrain/force/pressure, use of piezoresistive sensors allows morereliable detection of input strain/force/pressure.

In some embodiments, an example system for detecting a location of atouch input on a surface of a propagating medium includes a transmittercoupled to a propagating medium and configured to emit a signal. Thesignal has been allowed to propagate through a propagating medium and alocation of a touch input on a surface of the propagating medium isdetected at least in part by detecting an effect of the touch input onthe signal that has been allowed to propagate through the propagatingmedium. The example system also includes a piezoresistive sensor coupledto the propagating medium, wherein the piezoresistive sensor isconfigured to at least detect a force of the touch input on thepropagating medium.

In some embodiments, the system shown in FIG. 7A is included in a kiosk,an ATM, a computing device, an entertainment device, a digital signageapparatus, a cell phone, a tablet computer, a point of sale terminal, afood and restaurant apparatus, a gaming device, a casino game andapplication, a piece of furniture, a vehicle, an industrial application,a financial application, a medical device, an appliance, and any otherobjects or devices having surfaces. Propagating signal medium 702 iscoupled to transmitters 704, 706, 708, and 710 and receivers/sensors712, 714, 716, and 718. The locations where transmitters 704, 706, 708,and 710 and sensors 712, 714, 716, and 718 have been coupled topropagating signal medium 702, as shown in FIG. 7, are merely anexample. Other configurations of transmitter and sensor locations mayexist in various embodiments. Although FIG. 7A shows sensors locatedadjacent to transmitters, sensors may be located apart from transmittersin other embodiments. In some embodiments, a single transducer is usedas both a transmitter and a sensor. In various embodiments, thepropagating medium includes one or more of the following: panel, table,glass, screen, door, floor, whiteboard, plastic, wood, steel, metal,semiconductor, insulator, conductor, and any medium that is able topropagate an acoustic or ultrasonic signal. For example, medium 702 isglass of a display screen. A first surface of medium 702 includes asurface area where a user may touch to provide a selection input and asubstantially opposite surface of medium 702 is coupled to thetransmitters and sensors shown in FIG. 7A. In various embodiments, asurface of medium 702 is substantially flat, curved, or combinationsthereof and may be configured in a variety of shapes such asrectangular, square, oval, circular, trapezoidal, annular, or anycombination of these, and the like.

Examples of transmitters 704, 706, 708, and 710 include piezoelectrictransducers, piezoresistive elements/transmitters, electromagnetictransducers, transmitters, sensors, and/or any other transmitters andtransducers capable of propagating a signal through medium 702.

Examples of sensors 712, 714, 716, and 718 include piezoelectrictransducers, electromagnetic transducers, piezoresistivesensors/receivers (e.g., including bridge structure 100 of FIG. 1,sensor chip 200, etc.), laser vibrometer transmitters, and/or any othersensors and transducers capable of detecting a signal on medium 702. Insome embodiments, the transmitters and sensors shown in FIG. 7A arecoupled to medium 702 in a manner that allows a user's input to bedetected in a predetermined region of medium 702. Although fourtransmitters and four sensors are shown, any number of transmitters andany number of sensors may be used in other embodiments. For example, twotransmitters and three sensors may be used. In some embodiments, asingle transducer acts as both a transmitter and a sensor. For example,transmitter 704 and sensor 712 represent a single piezoelectrictransducer. In the example shown, transmitters 704, 706, 708, and 710each may propagate a signal through medium 702. A signal emitted by atransmitter is distinguishable from another signal emitted by anothertransmitter. In order to distinguish the signals, a phase of the signals(e.g., code division multiplexing), a frequency range of the signals(e.g., frequency division multiplexing), or a timing of the signals(e.g., time division multiplexing) may be varied. One or more of sensors712, 714, 716, and 718 receive the propagated signals. In anotherembodiment, the transmitters/sensors in FIG. 7A are attached to aflexible cable coupled to medium 102 via an encapsulant and/or gluematerial and/or fasteners.

Touch detector 720 is connected to the transmitters and sensors shown inFIG. 7. In some embodiments, detector 720 includes one or more of thefollowing: an integrated circuit chip, a printed circuit board, aprocessor, and other electrical components and connectors. Detector 720determines and sends signals to be propagated by transmitters 704, 706,708, and 710. Detector 720 also receives the signals detected by sensors712, 714, 716, and 718. The received signals are processed by detector720 to determine whether a disturbance associated with a user input hasbeen detected at a location on a surface of medium 702 associated withthe disturbance. Detector 720 is in communication with applicationsystem 722. Application system 722 uses information provided by detector720. For example, application system 722 receives from detector 720 acoordinate associated with a user touch input that is used byapplication system 722 to control a software application of applicationsystem 722. In some embodiments, application system 722 includes aprocessor and/or memory/storage. In other embodiments, detector 720 andapplication system 722 are at least in part included/processed in asingle processor. An example of data provided by detector 720 toapplication system 722 includes one or more of the following associatedwith a user indication: a location coordinate of a surface of medium702, a gesture, simultaneous user indications (e.g., multi-touch input),a time, a status, a direction, a velocity, a force magnitude, aproximity magnitude, a pressure, a size, and other measurable or derivedinformation.

FIGS. 7B-7D show different embodiments of transmitter and sensorcomponent arrangements utilized to detect a touch input along a surfacearea (e.g., to detect touch input on a touchscreen display). For exampleFIGS. 7B-7D show different arrangements of the transmitters and sensorsshown in FIG. 7A. In various embodiments, at least a portion of thetransmitter and sensor components shown in FIGS. 7B-7D are connected totouch detector 720. Connections between transmitter and sensorcomponents in FIGS. 7B-7D and touch detector 720 have not been shown inFIGS. 7B-7D. Other components (e.g., application system 722) connectedto touch detector 720 also have not been shown in FIGS. 7B-7D.Components are not drawn to scale. A piezoelectric transmitter is shownas a box labeled with a “T.” A piezoelectric sensor is shown as a boxlabeled with an “S.” A piezoresistive sensor is shown as a circlelabeled with an “S.” In some embodiments, the shown piezoelectrictransmitters and sensors are coupled to an inside surface border of aglass cover of a touchscreen display. In some embodiments, the shownpiezoresistive sensors are coupled behind a display panel (e.g., behindLED/OLED panel). The number of transmitters and sensors shown in FIGS.7B-7D are merely an example and any number of any type of transmittersand sensors may exist in various embodiments.

In some embodiments, a device includes one or more piezoelectrictransmitters and one or more piezoelectric receivers/sensors to detecttouch input location (e.g., coupled to the glass of the touch screen,coupled to side of metal housing of a device to detect touch inputlocation on device side, etc.) as well as an array of piezoresistivesensors to detect touch input force/pressure (e.g., array ofpiezoresistive sensors coupled behind LED/OLED display panel to detectmagnitude of deformation of the panel due to touch input, or one or morepiezoresistive sensors coupled to the inside of a device housing todetect grip force, etc.). Transmitter and sensor arrangement 730 shownin FIG. 7B includes piezoelectric transmitters/sensors around a borderarea of a propagating/touch input medium and an array of piezoresistivesensors.

In some embodiments, given the increased piezoresistive sensorsensitivity using the improvements described herein, one or morepiezoresistive sensors are utilized to receive/detect propagatedultrasonic touch input medium signals for touch input locationdetection. The same piezoresistive sensors may also be used to detectphysical disturbance magnitude as well. For example, an output signalfrom the piezoresistive sensor is first analyzed and correlated with itsinput supply voltage signal to detect the physical disturbance magnitude(e.g., using the process of FIG. 6), then when the propagated ultrasonicsignal is detected after propagation through the touch input medium, theoutput signal (e.g., delayed signal) from the piezoresistive sensor isanalyzed and correlated with an expected baseline propagated signal todetect a propagation delay caused by the touch input in determining theassociated touch input location (e.g., using the process of FIG. 10and/or FIG. 16). Thus the same output signal from a piezoresistivesensor can be used to both detect touch force and touch location (e.g.,by the same signal processing component: touch detector 720). Examplesensor configurations for devices including piezoelectric transmittersand piezoresistive sensors without piezoelectric sensors are shown inarrangement 740 of FIG. 7C.

In some embodiments, piezoresistive sensors are utilized to detect atouch input location without a use of piezoelectric transmitters. Forexample, given an array of piezoresistive sensors, a location of a touchinput is triangulated based on the detected physical disturbancemagnitudes and the relative locations of the sensors that detected thevarious magnitudes (e.g., using a matched filter). Example sensorconfigurations for devices including piezoresistive sensors withoutpiezoelectric transmitters are shown in arrangement 750 of FIG. 7D.

In some embodiments, data from piezoelectric transmitters/sensors anddata from piezoresistive sensors are used to complement and augment eachother. A touch input location information detected using piezoelectrictransmitters/sensors may be used to cross qualify physical disturbancemagnitude information from piezoresistive sensors. For example, when itis detected (using piezoresistive sensor data) that a touch input isbeing provided with low force, pressure, strain, etc. (e.g., user iswearing a glove that absorbs force), a piezoelectric transmitter gainand/or sensor sensitivity is increased to enable better touch inputlocation detection. In another example, if a sufficient physicaldisturbance magnitude is detected but a touch input location is notdetected (or touch input location is detected in a specific signaturepattern), then it may be concluded that the detected input is a resultof device bending (e.g., in a pocket) rather than as a result of anintended user interaction.

FIG. 8 is a block diagram illustrating an embodiment of a system fordetecting a touch input. In some embodiments, touch detector 802 isincluded in touch detector 720 of FIGS. 7A-7D. In some embodiments, thesystem of FIG. 8 is integrated in an integrated circuit chip. In someembodiments, signal processor component 410 of FIG. 4 and/or signalprocessor component 510 of FIG. 5 includes touch detector 802. Forexample, touch detector 802 shows the components of thetransmitter/receiver included in signal processor component 410 and/or510. In some embodiments, touch detector 802 is utilized as signalprocessor component 410 and/or 510.

Touch detector 802 includes system clock 804 that provides a synchronoussystem time source to one or more other components of detector 802.Controller 810 controls data flow and/or commands between microprocessor806, interface 808, DSP engine 820, and signal generator 812. In someembodiments, microprocessor 806 processes instructions and/orcalculations that can be used to program software/firmware and/orprocess data of detector 802. In some embodiments, a memory is coupledto microprocessor 806 and is configured to provide microprocessor 806with instructions.

Signal generator 812 generates signals to be used to propagate signalssuch as signals propagated by transmitters 704, 706, 708, and 710 ofFIG. 7A. For example, signal generator 812 generates pseudorandom binarysequence signals that are converted from digital to analog signals.Different signals (e.g., a different signal for each transmitter) may begenerated by signal generator 812 by varying a phase of the signals(e.g., code division multiplexing), a frequency range of the signals(e.g., frequency division multiplexing), or a timing of the signals(e.g., time division multiplexing). In some embodiments, spectralcontrol (e.g., signal frequency range control) of the signal generatedby signal generator 812 is performed. For example, microprocessor 806,DSP engine 820, and/or signal generator 812 determines a windowingfunction and/or amplitude modulation to be utilized to control thefrequencies of the signal generated by signal generator 812. Examples ofthe windowing function include a Hanning window and raised cosinewindow. Examples of the amplitude modulation include signal sidebandmodulation and vestigial sideband modulation. In some embodiments, thedetermined windowing function may be utilized by signal generator 812 togenerate a signal to be modulated to a carrier frequency. The carrierfrequency may be selected such that the transmitted signal is anultrasonic signal. For example, the transmitted signal to be propagatedthrough a propagating medium is desired to be an ultrasonic signal tominimize undesired interference with sonic noise and minimize excitationof undesired propagation modes of the propagating medium. The modulationof the signal may be performed using a type of amplitude modulation suchas signal sideband modulation and vestigial sideband modulation toperform spectral of the signal. The modulation may be performed bysignal generator 812 and/or driver 814. Driver 814 receives the signalfrom generator 812 and drives one or more transmitters, such astransmitters shown in FIGS. 7A-7C, to propagate signals through amedium.

A signal detected from a sensor such as a sensor shown in FIGS. 7A-7D isreceived by detector 802 and signal conditioner 816 conditions (e.g.,filters) the received analog signal for further processing. For example,signal conditioner 816 receives the signal outputted by driver 814 andperforms echo cancellation of the signal received by signal conditioner816. The conditioned signal is converted to a digital signal byanalog-to-digital converter 818. The converted signal is processed bydigital signal processor engine 820. For example, DSP engine 820separates components corresponding to different signals propagated bydifferent transmitters from the received signal and each component iscorrelated against a reference signal. The result of the correlation maybe used by microprocessor 806 to determine a location associated with auser touch input. For example, microprocessor 806 compares relativedifferences of disturbances detected in signals originating fromdifferent transmitters and/or received at different receivers/sensors todetermine the location.

In some embodiments, DSP engine 820 correlates the converted signalagainst a reference signal to determine a time domain signal thatrepresents a time delay caused by a touch input on a propagated signal.In some embodiments, DSP engine 820 performs dispersion compensation.For example, the time delay signal that results from correlation iscompensated for dispersion in the touch input surface medium andtranslated to a spatial domain signal that represents a physicaldistance traveled by the propagated signal disturbed by the touch input.In some embodiments, DSP engine 820 performs base pulse correlation. Forexample, the spatial domain signal is filtered using a match filter toreduce noise in the signal. A result of DSP engine 820 may be used bymicroprocessor 806 to determine a location associated with a user touchinput. For example, microprocessor 806 determines a hypothesis locationwhere a touch input may have been received and calculates an expectedsignal that is expected to be generated if a touch input was received atthe hypothesis location and the expected signal is compared with aresult of DSP engine 820 to determine whether a touch input was providedat the hypothesis location.

Interface 808 provides an interface for microprocessor 806 andcontroller 810 that allows an external component to access and/orcontrol detector 802. For example, interface 808 allows detector 802 tocommunicate with application system 722 of FIG. 7A and provides theapplication system with location information associated with a usertouch input (e.g., location, force, etc.).

FIG. 9 is a flow chart illustrating an embodiment of a process forcalibrating and validating touch detection. In some embodiments, theprocess of FIG. 9 is used at least in part to calibrate and validate thesystem of FIGS. 7A-7D and/or the system of FIG. 8. At 902, locations ofsignal transmitters and sensors with respect to a surface aredetermined. For example, locations of transmitters and sensors shown inFIGS. 7A-7D are determined with respect to their location on a surfaceof medium 702. In some embodiments, determining the locations includesreceiving location information. In various embodiments, one or more ofthe locations may be fixed and/or variable.

At 904, signal transmitters and sensors are calibrated. In someembodiments, calibrating the transmitter includes calibrating acharacteristic of a signal driver and/or transmitter (e.g., strength).In some embodiments, calibrating the sensor includes calibrating acharacteristic of a sensor (e.g., sensitivity). In some embodiments, thecalibration of 904 is performed to optimize the coverage and improvesignal-to-noise transmission/detection of a signal (e.g., acoustic orultrasonic) to be propagated through a medium and/or a disturbance to bedetected. For example, one or more components of the system of FIGS.7A-7D and/or the system of FIG. 8 are tuned to meet a signal-to-noiserequirement. In some embodiments, the calibration of 904 depends on thesize and type of a transmission/propagation medium and geometricconfiguration of the transmitters/sensors. In some embodiments, thecalibration of step 904 includes detecting a failure or aging of atransmitter or sensor. In some embodiments, the calibration of step 904includes cycling the transmitter and/or receiver. For example, toincrease the stability and reliability of a piezoelectric transmitterand/or receiver, a burn-in cycle is performed using a burn-in signal. Insome embodiments, the step of 904 includes configuring at least onesensing device within a vicinity of a predetermined spatial region tocapture an indication associated with a disturbance using the sensingdevice. The disturbance is caused in a selected portion of the inputsignal corresponding to a selection portion of the predetermined spatialregion.

At 906, surface disturbance detection is calibrated. In someembodiments, a test signal is propagated through a medium such as medium702 of FIG. 7A to determine an expected sensed signal when nodisturbance has been applied. In some embodiments, a test signal ispropagated through a medium to determine a sensed signal when one ormore predetermined disturbances (e.g., predetermined touch) are appliedat a predetermined location. Using the sensed signal, one or morecomponents may be adjusted to calibrate the disturbance detection. Insome embodiments, the test signal is used to determine a signal that canbe later used to process/filter a detected signal disturbed by a touchinput.

In some embodiments, data determined using one or more steps of FIG. 9is used to determine data (e.g., formula, variable, coefficients, etc.)that can be used to calculate an expected signal that would result whena touch input is provided at a specific location on a touch inputsurface. For example, one or more predetermined test touch disturbancesare applied at one or more specific locations on the touch input surfaceand a test propagating signal that has been disturbed by the test touchdisturbance is used to determine the data (e.g., transmitter/sensorparameters) that is to be used to calculate an expected signal thatwould result when a touch input is provided at the one or more specificlocations.

At 908, a validation of a touch detection system is performed. Forexample, the systems of FIGS. 7A-7D and/or FIG. 8 are tested usingpredetermined disturbance patterns to determine detection accuracy,detection resolution, multi-touch detection, and/or response time. Ifthe validation fails, the process of FIG. 9 may be at least in partrepeated and/or one or more components may be adjusted before performinganother validation.

FIG. 10 is a flow chart illustrating an embodiment of a process fordetecting a user touch input. In some embodiments, the process of FIG.10 is at least in part implemented on touch detector 720 of FIGS. 7A-7Dand/or touch detector 802 of FIG. 8.

At 1002, a signal that can be used to propagate an active signal througha surface region is sent. In some embodiments, sending the signalincludes driving (e.g., using driver 814 of FIG. 8) a transmitter suchas a transducer (e.g., transmitter 704 of FIG. 7A) to propagate anactive signal (e.g., acoustic or ultrasonic) through a propagatingmedium with the surface region. In some embodiments, the signal includesa sequence selected to optimize autocorrelation (e.g., resulting innarrow/short peaks) of the signal. For example, the signal includes aZadoff-Chu sequence. In some embodiments, the signal includes apseudorandom binary sequence with or without modulation. In someembodiments, the propagated signal is an acoustic signal. In someembodiments, the propagated signal is an ultrasonic signal (e.g.,outside the range of human hearing). For example, the propagated signalis a signal above 20 kHz (e.g., within the range between 80 kHz to 100kHz). In other embodiments, the propagated signal may be within therange of human hearing. In some embodiments, by using the active signal,a user input on or near the surface region can be detected by detectingdisturbances in the active signal when it is received by a sensor on thepropagating medium. By using an active signal rather than merelylistening passively for a user touch indication on the surface, othervibrations and disturbances that are not likely associated with a usertouch indication can be more easily discerned/filtered out. In someembodiments, the active signal is used in addition to receiving apassive signal from a user input to determine the user input.

When attempting to propagate signal through a medium such as glass inorder to detect touch inputs on the medium, the range of frequenciesthat may be utilized in the transmitted signal determines the bandwidthrequired for the signal as well as the propagation mode of the mediumexcited by the signal and noise of the signal.

With respect to bandwidth, if the signal includes more frequencycomponents than necessary to achieve a desired function, then the signalis consuming more bandwidth than necessary, leading to wasted resourceconsumption and slower processing times.

With respect to the propagation modes of the medium, a propagationmedium such as a glass likes to propagate a signal (e.g., anultrasonic/sonic signal) in certain propagation modes. For example, inthe A0 propagation mode of glass the propagated signal travels in wavesup and down perpendicular to a surface of the glass (e.g., by bendingthe glass) whereas in the S0 propagation mode of glass the propagatedsignal travels in waves up and down parallel to the glass (e.g., bycompressing and expanding the glass). A0 mode is desired over S0 mode intouch detection because a touch input contact on a glass surfacedisturbs the perpendicular bending wave of the A0 mode and the touchinput does not significantly disturb the parallel compression waves ofthe S0 mode. The example glass medium has higher order propagation modessuch as A1 mode and S1 mode that become excited with differentfrequencies of the propagated signals.

With respect to the noise of the signal, if the propagated signal is inthe audio frequency range of humans, a human user would be able to hearthe propagated signal and may detract from the user's user experience.If the propagated signal included frequency components that excitedhigher order propagation modes of the propagating medium, the signal maycreate undesirable noise within the propagating medium that makesdetection of touch input disturbances of the propagated signal difficultto achieve.

In some embodiments, the sending the signal includes performing spectralcontrol of the signal. In some embodiments, performing spectral controlon the signal includes controlling the frequencies included in thesignal. In order to perform spectral control, a windowing function(e.g., Hanning window, raised cosine window, etc.) and/or amplitudemodulation (e.g., signal sideband modulation, vestigial sidebandmodulation, etc.) may be utilized. In some embodiments, spectral controlis performed to attempt to only excite A0 propagation mode of thepropagation medium. In some embodiments, spectral control is performedto limit the frequency range of the propagated signal to be within 50kHz to 250 kHz.

In some embodiments, the sent signal includes a pseudorandom binarysequence. The binary sequence may be represented using a square pulse.However, modulated signal of the square pulse includes a wide range offrequency components due to the sharp square edges of the square pulse.In order to efficiently transmit the pseudorandom binary sequence, it isdesirable to “smooth out” sharp edges of the binary sequence signal byutilizing a shaped pulse. A windowing function may be utilized to“smooth out” the sharp edges and reduce the frequency range of thesignal. A windowing function such as Hanning window and/or raised cosinewindow may be utilized. In some embodiments, the type and/or one or moreparameters of the windowing function is determined based at least inpart on a property of a propagation medium such as medium 702 of FIG.7A. For example, information about propagation modes and associatedfrequencies of the propagation medium is utilized to select the typeand/or parameter(s) of the windowing function (e.g., to excite desiredpropagation mode and not excite undesired propagation mode). In someembodiments, a type of propagation medium is utilized to select the typeand/or parameter(s) of the windowing function. In some embodiments, adispersion coefficient, a size, a dimension, and/or a thickness of thepropagation medium is utilized to select the type and/or parameter(s) ofthe windowing function. In some embodiments, a property of a transmitteris utilized to select the type and/or parameter(s) of the windowingfunction.

In some embodiments, sending the signal includes modulating (e.g.,utilize amplitude modulation) the signal. For example, the desiredbaseband signal (e.g., a pseudorandom binary sequence signal) is desiredto be transmitted at a carrier frequency (e.g., ultrasonic frequency).In this example, the amplitude of the signal at the carrier frequencymay be varied to send the desired baseband signal (e.g., utilizingamplitude modulation). However, traditional amplitude modulation (e.g.,utilizing double-sideband modulation) produces an output signal that hastwice the frequency bandwidth of the original baseband signal.Transmitting this output signal consumes resources that otherwise do nothave to be utilized. In some embodiments, single-sideband modulation isutilized. In some embodiments, in single-sideband modulation, the outputsignal utilizes half of the frequency bandwidth of double-sidebandmodulation by not utilizing a redundant second sideband included in thedouble-sideband modulated signal. In some embodiments, vestigialsideband modulation is utilized. For example, a portion of one of theredundant sidebands is effectively removed from a correspondingdouble-sideband modulated signal to form a vestigial sideband signal. Insome embodiments, double-sideband modulation is utilized.

In some embodiments, sending the signal includes determining the signalto be transmitted by a transmitter such that the signal isdistinguishable from other signal(s) transmitted by other transmitters.In some embodiments, sending the signal includes determining a phase ofthe signal to be transmitted (e.g., utilize code divisionmultiplexing/CDMA). For example, an offset within a pseudorandom binarysequence to be transmitted is determined. In this example, eachtransmitter (e.g., transmitters 704, 706, 708, and 710 of FIG. 7A)transmits a signal with the same pseudorandom binary sequence but with adifferent phase/offset. The signal offset/phase difference between thesignals transmitted by the transmitters may be equally spaced (e.g.,64-bit offset for each successive signal) or not equally spaced (e.g.,different offset signals). The phase/offset between the signals may beselected such that it is long enough to reliably distinguish betweendifferent signals transmitted by different transmitters. In someembodiments, the signal is selected such that the signal isdistinguishable from other signals transmitted and propagated throughthe medium. In some embodiments, the signal is selected such that thesignal is orthogonal to other signals (e.g., each signal orthogonal toeach other) transmitted and propagated through the medium.

In some embodiments, sending the signal includes determining a frequencyof the signal to be transmitted (e.g., utilize frequency divisionmultiplexing/FDMA). For example, a frequency range to be utilized forthe signal is determined. In this example, each transmitter (e.g.,transmitters of FIGS. 7A-7C) transmits a signal in a different frequencyrange as compared to signals transmitted by other transmitters. Therange of frequencies that can be utilized by the signals transmitted bythe transmitters is divided among the transmitters. In some cases if therange of frequencies that can be utilized by the signals is small, itmay be difficult to transmit all of the desired different signals of allthe transmitters. Thus the number of transmitters that can be utilizedwith frequency division multiplexing/FDMA may be smaller than can beutilized with code division multiplexing/CDMA.

In some embodiments, sending the signal includes determining a timing ofthe signal to be transmitted (e.g., utilize time divisionmultiplexing/TDMA). For example, a time when the signal should betransmitted is determined. In this example, each transmitter (e.g.,transmitters of FIGS. 7A-7C) transmits a signal in different time slotsas compared to signals transmitted by other transmitters. This may allowthe transmitters to transmit signals in a round-robin fashion such thatonly one transmitter is emitting/transmitting at one time. A delayperiod may be inserted between periods of transmission of differenttransmitters to allow the signal of the previous transmitter tosufficiently dissipate before transmitting a new signal of the nexttransmitter. In some cases, time division multiplexing/TDMA may bedifficult to utilize in cases where fast detection of touch input isdesired because time division multiplexing/TDMA slows down the speed oftransmission/detection as compared to code division multiplexing/CDMA.

At 1004, the active signal that has been disturbed by a disturbance ofthe surface region is received. The disturbance may be associated with auser touch indication. In some embodiments, the disturbance causes theactive signal that is propagating through a medium to be attenuatedand/or delayed. In some embodiments, the disturbance in a selectedportion of the active signal corresponds to a location on the surfacethat has been indicated (e.g., touched) by a user.

At 1006, the received signal is processed to at least in part determinea location associated with the disturbance. In some embodiments,determining the location includes extracting a desired signal from thereceived signal at least in part by removing or reducing undesiredcomponents of the received signal such as disturbances caused byextraneous noise and vibrations not useful in detecting a touch input.In some embodiments, components of the received signal associated withdifferent signals of different transmitters are separated. For example,different signals originating from different transmitters are isolatedfrom other signals of other transmitters for individual processing. Insome embodiments, determining the location includes comparing at least aportion of the received signal (e.g., signal component from a singletransmitter) to a reference signal (e.g., reference signal correspondingto the transmitter signal) that has not been affected by thedisturbance. The result of the comparison may be used with a result ofother comparisons performed using the reference signal and othersignal(s) received at a plurality of sensors.

In some embodiments, receiving the received signal and processing thereceived signal are performed on a periodic interval. For example, thereceived signal is captured in 5 ms intervals and processed. In someembodiments, determining the location includes extracting a desiredsignal from the received signal at least in part by removing or reducingundesired components of the received signal such as disturbances causedby extraneous noise and vibrations not useful in detecting a touchinput. In some embodiments, determining the location includes processingthe received signal and comparing the processed received signal with acalculated expected signal associated with a hypothesis touch contactlocation to determine whether a touch contact was received at thehypothesis location of the calculated expected signal. Multiplecomparisons may be performed with various expected signals associatedwith different hypothesis locations until the expected signal that bestmatches the processed received signal is found and the hypothesislocation of the matched expected signal is identified as the touchcontact location(s) of a touch input. For example, signals received bysensors (e.g., sensors of FIGS. 7A-7D) from various transmitters (e.g.,transmitters of FIGS. 7A-7C) are compared with corresponding expectedsignals to determine a touch input location (e.g., single or multi-touchlocations) that minimizes the overall difference between all respectivereceived and expected signals.

The location, in some embodiments, is a location (e.g., a locationcoordinate) on the surface region where a user has provided a touchinput. In addition to determining the location, one or more of thefollowing information associated with the disturbance may be determinedat 1006: a gesture, simultaneous user indications (e.g., multi-touchinput), a time, a status, a direction, a velocity, a force magnitude, aproximity magnitude, a pressure, a size, and other measurable or derivedinformation. In some embodiments, the location is not determined at 1006if a location cannot be determined using the received signal and/or thedisturbance is determined to be not associated with a user input.Information determined at 1006 may be provided and/or outputted.

Although FIG. 10 shows receiving and processing an active signal thathas been disturbed, in some embodiments, a received signal has not beendisturbed by a touch input and the received signal is processed todetermine that a touch input has not been detected. An indication that atouch input has not been detected may be provided/outputted.

FIG. 11 is a flow chart illustrating an embodiment of a process fordetermining a location associated with a disturbance on a surface. Insome embodiments, the process of FIG. 11 is included in 1006 of FIG. 10.The process of FIG. 11 may be implemented in touch detector 720 of FIGS.7A-7D and/or touch detector 802 of FIG. 8. In some embodiments, at leasta portion of the process of FIG. 11 is repeated for each combination oftransmitter and sensor pair. For example, for each active signaltransmitted by a transmitter (e.g., transmitted by transmitter of FIGS.7A-7C), at least a portion of the process of FIG. 11 is repeated foreach sensor (e.g., sensors of FIGS. 7A-7D) receiving the active signal.In some embodiments, the process of FIG. 11 is performed periodically(e.g., 5 ms periodic interval).

At 1102, a received signal is conditioned. In some embodiments, thereceived signal is a signal including a pseudorandom binary sequencethat has been freely propagated through a medium with a surface that canbe used to receive a user input. For example, the received signal is thesignal that has been received at 1004 of FIG. 10. In some embodiments,conditioning the signal includes filtering or otherwise modifying thereceived signal to improve signal quality (e.g., signal-to-noise ratio)for detection of a pseudorandom binary sequence included in the receivedsignal and/or user touch input. In some embodiments, conditioning thereceived signal includes filtering out from the signal extraneous noiseand/or vibrations not likely associated with a user touch indication.

At 1104, an analog to digital signal conversion is performed on thesignal that has been conditioned at 1102. In various embodiments, anynumber of standard analog to digital signal converters may be used.

At 1106, a time domain signal capturing a received signal time delaycaused by a touch input disturbance is determined. In some embodiments,determining the time domain signal includes correlating the receivedsignal (e.g., signal resulting from 1104) to locate a time offset in theconverted signal (e.g., perform pseudorandom binary sequencedeconvolution) where a signal portion that likely corresponds to areference signal (e.g., reference pseudorandom binary sequence that hasbeen transmitted through the medium) is located. For example, a resultof the correlation can be plotted as a graph of time within the receivedand converted signal (e.g., time-lag between the signals) vs. a measureof similarity. In some embodiments, performing the correlation includesperforming a plurality of correlations. For example, a coarsecorrelation is first performed then a second level of fine correlationis performed. In some embodiments, a baseline signal that has not beendisturbed by a touch input disturbance is removed in the resulting timedomain signal. For example, a baseline signal representing a measuredsignal (e.g., a baseline time domain signal) associated with a receivedactive signal that has not been disturbed by a touch input disturbanceis subtracted from a result of the correlation to further isolateeffects of the touch input disturbance by removing components of thesteady state baseline signal not affected by the touch inputdisturbance.

At 1108, the time domain signal is converted to a spatial domain signal.In some embodiments, converting the time domain signal includesconverting the time domain signal determined at 1106 into a spatialdomain signal that translates the time delay represented in the timedomain signal to a distance traveled by the received signal in thepropagating medium due to the touch input disturbance. For example, atime domain signal that can be graphed as time within the received andconverted signal vs. a measure of similarity is converted to a spatialdomain signal that can be graphed as distance traveled in the medium vs.the measure of similarity.

In some embodiments, performing the conversion includes performingdispersion compensation. For example, using a dispersion curvecharacterizing the propagating medium, time values of the time domainsignal are translated to distance values in the spatial domain signal.In some embodiments, a resulting curve of the time domain signalrepresenting a distance likely traveled by the received signal due to atouch input disturbance is narrower than the curve contained in the timedomain signal representing the time delay likely caused by the touchinput disturbance. In some embodiments, the time domain signal isfiltered using a match filter to reduce undesired noise in the signal.For example, using a template signal that represents an ideal shape of aspatial domain signal, the converted spatial domain signal is matchfiltered (e.g., spatial domain signal correlated with the templatesignal) to reduce noise not contained in the bandwidth of the templatesignal. The template signal may be predetermined (e.g., determined at906 of FIG. 9) by applying a sample touch input to a touch input surfaceand measuring a received signal.

At 1110, the spatial domain signal is compared with one or more expectedsignals to determine a touch input captured by the received signal. Insome embodiments, comparing the spatial domain signal with the expectedsignal includes generating expected signals that would result if a touchcontact was received at hypothesis locations. For example, a hypothesisset of one or more locations (e.g., single touch or multi-touchlocations) where a touch input might have been received on a touch inputsurface is determined, and an expected spatial domain signal that wouldresult at 1108 if touch contacts were received at the hypothesis set oflocation(s) is determined (e.g., determined for a specific transmitterand sensor pair using data measured at 906 of FIG. 9). The expectedspatial domain signal may be compared with the actual spatial signaldetermined at 1108. The hypothesis set of one or more locations may beone of a plurality of hypothesis sets of locations (e.g., exhaustive setof possible touch contact locations on a coordinate grid dividing atouch input surface).

The proximity of location(s) of a hypothesis set to the actual touchcontact location(s) captured by the received signal may be proportionalto the degree of similarity between the expected signal of thehypothesis set and the spatial signal determined at 1108. In someembodiments, signals received by sensors (e.g., sensors of FIGS. 7A-7D)from transmitters (e.g., transmitters of FIGS. 7A-7C) are compared withcorresponding expected signals for each sensor/transmitter pair toselect a hypothesis set that minimizes the overall difference betweenall respective detected and expected signals. In some embodiments, oncea hypothesis set is selected, another comparison between the determinedspatial domain signals and one or more new expected signals associatedwith finer resolution hypothesis touch location(s) (e.g., locations on anew coordinate grid with more resolution than the coordinate grid usedby the selected hypothesis set) near the location(s) of the selectedhypothesis set is determined.

FIG. 12 is a flow chart illustrating an embodiment of a process fordetermining time domain signal capturing of a disturbance caused by atouch input. In some embodiments, the process of FIG. 12 is included in1106 of FIG. 11. The process of FIG. 12 may be implemented in touchdetector 720 of FIGS. 7A-7D and/or touch detector 802 of FIG. 8.

At 1202, a first correlation is performed. In some embodiments,performing the first correlation includes correlating a received signal(e.g., resulting converted signal determined at 1104 of FIG. 11) with areference signal. Performing the correlation includes cross-correlatingor determining a convolution (e.g., interferometry) of the convertedsignal with a reference signal to measure the similarity of the twosignals as a time-lag is applied to one of the signals. By performingthe correlation, the location of a portion of the converted signal thatmost corresponds to the reference signal can be located. For example, aresult of the correlation can be plotted as a graph of time within thereceived and converted signal (e.g., time-lag between the signals) vs. ameasure of similarity. The associated time value of the largest value ofthe measure of similarity corresponds to the location where the twosignals most correspond. By comparing this measured time value against areference time value (e.g., at 906 of FIG. 9) not associated with atouch indication disturbance, a time delay/offset or phase differencecaused on the received signal due to a disturbance caused by a touchinput can be determined. In some embodiments, by measuring theamplitude/intensity difference of the received signal at the determinedtime vs. a reference signal, a force associated with a touch indicationmay be determined. In some embodiments, the reference signal isdetermined based at least in part on the signal that was propagatedthrough a medium (e.g., based on a source pseudorandom binary sequencesignal that was propagated). In some embodiments, the reference signalis at least in part determined using information determined duringcalibration at 906 of FIG. 9. The reference signal may be chosen so thatcalculations required to be performed during the correlation may besimplified. For example, the reference signal is a simplified referencesignal that can be used to efficiently correlate the reference signalover a relatively large time difference (e.g., lag-time) between thereceived and converted signal and the reference signal.

At 1204, a second correlation is performed based on a result of thefirst correlation. Performing the second correlation includescorrelating (e.g., cross-correlation or convolution similar to step1202) a received signal (e.g., resulting converted signal determined at1104 of FIG. 11) with a second reference signal. The second referencesignal is a more complex/detailed (e.g., more computationally intensive)reference signal as compared to the first reference signal used in 1202.In some embodiments, the second correlation is performed because usingthe second reference signal in 1202 may be too computationally intensivefor the time interval required to be correlated in 1202. Performing thesecond correlation based on the result of the first correlation includesusing one or more time values determined as a result of the firstcorrelation. For example, using a result of the first correlation, arange of likely time values (e.g., time-lag) that most correlate betweenthe received signal and the first reference signal is determined and thesecond correlation is performed using the second reference signal onlyacross the determined range of time values to fine tune and determinethe time value that most corresponds to where the second referencesignal (and, by association, also the first reference signal) matchedthe received signal. In various embodiments, the first and secondcorrelations have been used to determine a portion within the receivedsignal that corresponds to a disturbance caused by a touch input at alocation on a surface of a propagating medium. In other embodiments, thesecond correlation is optional. For example, only a single correlationstep is performed. Any number of levels of correlations may be performedin other embodiments.

FIG. 13 is a flow chart illustrating an embodiment of a processcomparing spatial domain signals with one or more expected signals todetermine touch contact location(s) of a touch input. In someembodiments, the process of FIG. 13 is included in 1110 of FIG. 11. Theprocess of FIG. 13 may be implemented in touch detector 720 of FIGS.7A-7D and/or touch detector 802 of FIG. 8.

At 1302, a hypothesis of a number of simultaneous touch contactsincluded in a touch input is determined. In some embodiments, whendetecting a location of a touch contact, the number of simultaneouscontacts being made to a touch input surface (e.g., surface of medium702 of FIG. 7A) is desired to be determined. For example, it is desiredto determine the number of fingers touching a touch input surface (e.g.,single touch or multi-touch). In some embodiments, in order to determinethe number of simultaneous touch contacts, the hypothesis number isdetermined and the hypothesis number is tested to determine whether thehypothesis number is correct. In some embodiments, the hypothesis numberis initially determined as zero (e.g., associated with no touch inputbeing provided). In some embodiments, determining the hypothesis numberof simultaneous touch contacts includes initializing the hypothesisnumber to be a previously determined number of touch contacts. Forexample, a previous execution of the process of FIG. 13 determined thattwo touch contacts are being provided simultaneously and the hypothesisnumber is set as two. In some embodiments, determining the hypothesisnumber includes incrementing or decrementing a previously determinedhypothesis number of touch contacts. For example, a previouslydetermined hypothesis number is 2 and determining the hypothesis numberincludes incrementing the previously determined number and determiningthe hypothesis number as the incremented number (i.e., 3). In someembodiments, each time a new hypothesis number is determined, apreviously determined hypothesis number is iteratively incrementedand/or decremented unless a threshold maximum (e.g., 10) and/orthreshold minimum (e.g., 0) value has been reached.

At 1304, one or more hypothesis sets of one or more touch contactlocations associated with the hypothesis number of simultaneous touchcontacts are determined. In some embodiments, it is desired to determinethe coordinate locations of fingers touching a touch input surface. Insome embodiments, in order to determine the touch contact locations, oneor more hypothesis sets are determined on potential location(s) of touchcontact(s) and each hypothesis set is tested to determine whichhypothesis set is most consistent with a detected data.

In some embodiments, determining the hypothesis set of potential touchcontact locations includes dividing a touch input surface into aconstrained number of points (e.g., divide into a coordinate grid) wherea touch contact may be detected. For example, in order to initiallyconstrain the number of hypothesis sets to be tested, the touch inputsurface is divided into a coordinate grid with relatively large spacingbetween the possible coordinates. Each hypothesis set includes a numberof location identifiers (e.g., location coordinates) that match thehypothesis number determined in 1302. For example, if two was determinedto be the hypothesis number in 1302, each hypothesis set includes twolocation coordinates on the determined coordinate grid that correspondto potential locations of touch contacts of a received touch input. Insome embodiments, determining the one or more hypothesis sets includesdetermining exhaustive hypothesis sets that exhaustively cover allpossible touch contact location combinations on the determinedcoordinate grid for the determined hypothesis number of simultaneoustouch contacts. In some embodiments, a previously determined touchcontact location(s) of a previous determined touch input is initializedas the touch contact location(s) of a hypothesis set.

At 1306, a selected hypothesis set is selected among the one or morehypothesis sets of touch contact location(s) as best corresponding totouch contact locations captured by detected signal(s). In someembodiments, one or more propagated active signals (e.g., signaltransmitted at 1002 of FIG. 10) that have been disturbed by a touchinput on a touch input surface are received (e.g., received at 1004 ofFIG. 10) by one or more sensors such as sensors of FIGS. 7A-7D. Eachactive signal transmitted from each transmitter (e.g., different activesignals each transmitted by transmitters of FIGS. 7A-7C) is received byeach sensor (e.g., sensors of FIGS. 7A-7D) and may be processed todetermine a detected signal (e.g., spatial domain signal determined at1108 of FIG. 11) that characterizes a signal disturbance caused by thetouch input. In some embodiments, for each hypothesis set of touchcontact location(s), an expected signal is determined for each signalexpected to be received at one or more sensors. The expected signal maybe determined using a predetermined function that utilizes one or morepredetermined coefficients (e.g., coefficient determined for a specificsensor and/or transmitter transmitting a signal to be received at thesensor) and the corresponding hypothesis set of touch contactlocation(s). The expected signal(s) may be compared with correspondingdetected signal(s) to determine an indicator of a difference between allthe expected signal(s) for a specific hypothesis set and thecorresponding detected signals. By comparing the indicators for each ofthe one or more hypothesis sets, the selected hypothesis set may beselected (e.g., hypothesis set with the smallest indicated difference isselected).

At 1308, it is determined whether additional optimization is to beperformed. In some embodiments, determining whether additionaloptimization is to be performed includes determining whether any newhypothesis set(s) of touch contact location(s) should be analyzed inorder to attempt to determine a better selected hypothesis set. Forexample, a first execution of step 1306 utilizes hypothesis setsdetermined using locations on a larger distance increment coordinategrid overlaid on a touch input surface and additional optimization is tobe performed using new hypothesis sets that include locations from acoordinate grid with smaller distance increments. Additionaloptimizations may be performed any number of times. In some embodiments,the number of times additional optimizations are performed ispredetermined. In some embodiments, the number of times additionaloptimizations are performed is dynamically determined. For example,additional optimizations are performed until a comparison thresholdindicator value for the selected hypothesis set is reached and/or acomparison indicator for the selected hypothesis does not improve by athreshold amount. In some embodiments, for each optimization iteration,optimization may be performed for only a single touch contact locationof the selected hypothesis set and other touch contact locations of theselected hypothesis may be optimized in a subsequent iteration ofoptimization.

If at 1308 it is determined that additional optimization should beperformed, at 1310, one or more new hypothesis sets of one or more touchcontact locations associated with the hypothesis number of the touchcontacts are determined based on the selected hypothesis set. In someembodiments, determining the new hypothesis sets includes determininglocation points (e.g., more detailed resolution locations on acoordinate grid with smaller distance increments) near one of the touchcontact locations of the selected hypothesis set in an attempt to refinethe one of the touch contact locations of the selected hypothesis set.The new hypothesis sets may each include one of the newly determinedlocation points, and the other touch contact location(s), if any, of anew hypothesis set may be the same locations as the previously selectedhypothesis set. In some embodiments, the new hypothesis sets may attemptto refine all touch contact locations of the selected hypothesis set.The process proceeds back to 1306, whether or not a newly selectedhypothesis set (e.g., if previously selected hypothesis set still bestcorresponds to detected signal(s), the previously selected hypothesisset is retained as the new selected hypothesis set) is selected amongthe newly determined hypothesis sets of touch contact location(s).

If at 1308 it is determined that additional optimization should not beperformed, at 1312, it is determined whether a threshold has beenreached. In some embodiments, determining whether a threshold has beenreached includes determining whether the determined hypothesis number ofcontact points should be modified to test whether a different number ofcontact points has been received for the touch input. In someembodiments, determining whether the threshold has been reached includesdetermining whether a comparison threshold indicator value for theselected hypothesis set has been reached and/or a comparison indicatorfor the selected hypothesis did not improve by a threshold amount sincea previous determination of a comparison indicator for a previouslyselected hypothesis set. In some embodiments, determining whether thethreshold has been reached includes determining whether a thresholdamount of energy still remains in a detected signal after accounting forthe expected signal of the selected hypothesis set. For example, athreshold amount of energy still remains if an additional touch contactneeds be included in the selected hypothesis set.

If at 1312, it is determined that the threshold has not been reached,the process continues to 1302 where a new hypothesis number of touchinputs is determined. The new hypothesis number may be based on theprevious hypothesis number. For example, the previous hypothesis numberis incremented by one as the new hypothesis number.

If at 1312, it is determined that the threshold has been reached, at1314, the selected hypothesis set is indicated as the detectedlocation(s) of touch contact(s) of the touch input. For example, alocation coordinate(s) of a touch contact(s) is provided.

FIG. 14 is a flowchart illustrating an embodiment of a process forselecting a selected hypothesis set of touch contact location(s). Insome embodiments, the process of FIG. 14 is included in 1306 of FIG. 13.The process of FIG. 14 may be implemented in touch detector 720 of FIGS.7A-7D and/or touch detector 802 of FIG. 8.

At 1402, for each hypothesis set (e.g., determined at 1304 of FIG. 13),an expected signal that would result if a touch contact was received atthe contact location(s) of the hypothesis set is determined for eachdetected signal and for each touch contact location of the hypothesisset. In some embodiments, determining the expected signal includes usinga function and one or more function coefficients to generate/simulatethe expected signal. The function and/or one or more functioncoefficients may be predetermined (e.g., determined at 906 of FIG. 9)and/or dynamically determined (e.g., determined based on one or moreprovided touch contact locations). In some embodiments, the functionand/or one or more function coefficients may be determined/selectedspecifically for a particular transmitter and/or sensor of a detectedsignal. For example, the expected signal is to be compared to a detectedsignal and the expected signal is generated using a function coefficientdetermined specifically for the pair of transmitter and sensor of thedetected signal. In some embodiments, the function and/or one or morefunction coefficients may be dynamically determined.

In some embodiments, in the event the hypothesis set includes more thanone touch contact location (e.g., multi-touch input), expected signalfor each individual touch contact location is determined separately andcombined together. For example, an expected signal that would result ifa touch contact was provided at a single touch contact location is addedwith other single touch contact expected signals (e.g., effects frommultiple simultaneous touch contacts add linearly) to generate a singleexpected signal that would result if the touch contacts of the addedsignals were provided simultaneously.

In some embodiments, the expected signal for a single touch contact ismodeled as the function:C*P(x−d)

where C is a function coefficient (e.g., complex coefficient) and P(x)is a function and d is the total path distance between a transmitter(e.g., transmitter of a signal desired to be simulated) to a touch inputlocation and between the touch input location and a sensor (e.g.,receiver of the signal desired to be simulated).

In some embodiments, the expected signal for one or more touch contactsis modeled as the function:Σ_(j=1) ^(N) C _(j) P(x−d _(j))

where j indicates which touch contact and N is the number of totalsimultaneous touch contacts being modeled (e.g., hypothesis numberdetermined at 1302 of FIG. 13).

At 1404, corresponding detected signals are compared with correspondingexpected signals. In some embodiments, the detected signals includespatial domain signals determined at 1108 of FIG. 11. In someembodiments, comparing the signals includes determining a mean squareerror between the signals. In some embodiments, comparing the signalsincludes determining a cost function that indicates thesimilarity/difference between the signals. In some embodiments, the costfunction for a hypothesis set (e.g., hypothesis set determined at 1304of FIG. 13) analyzed for a single transmitter/sensor pair is modeled as:ε(r _(x) ,t _(x))=|q(x)−Σ_(j=1) ^(N) C _(j) P(x−d _(j))|²

where ε(r_(x), t_(x)) is the cost function, q(x) is the detected signal,and Σ_(j=1) ^(N)C_(j)P(x−d_(j)) is the expected signal. In someembodiments, the global cost function for a hypothesis set analyzed formore than one (e.g., all) transmitter/sensor pairs is modeled as:ε=Σ_(i=1) ^(Z)ε(r _(x) ,t _(x))_(i)

where ε is the global cost function, Z is the number of totaltransmitter/sensor pairs, i indicates the particular transmitter/sensorpair, and ε(r_(x), t_(x))_(i) is the cost function of the particulartransmitter/sensor pair.

At 1406, a selected hypothesis set of touch contact location(s) isselected among the one or more hypothesis sets of touch contactlocation(s) as best corresponding to detected signal(s). In someembodiments, the selected hypothesis set is selected among hypothesissets determined at 1304 or 1310 of FIG. 13. In some embodiments,selecting the selected hypothesis set includes determining the globalcost function (e.g., function ε described above) for each hypothesis setin the group of hypothesis sets and selecting the hypothesis set thatresults in the smallest global cost function value.

FIG. 15A is a diagram illustrating different views of a device withtouch input enabled housing. Front view 1530 of the device shows a frontdisplay surface of the device. Left side view 1534 of the device showsan example touch input external surface region 1540 on a sidewall of thedevice where a touch input is able to be detected. For example, alocation and a force of a user touch input are able to be detected inregion 1540 by detecting disturbances to transmitted signals in region1540. By touch enabling the side of the device, one or more functionstraditionally served by physical buttons are able to be provided withoutthe use of physical buttons. For example, volume control inputs are ableto be detected on the side without the use of physical volume controlbuttons. Right side view 1532 of the device shows touch input externalsurface region 1542 on another sidewall of the device where a user touchinput can be detected. Although regions 1540 and 1542 have been shown assmooth regions, in various other embodiments one or more physicalbuttons, ports, and/or openings (e.g., SIM/memory card tray) may exist,or the region can be textured to provide an indication of the sensingregion. Touch input detection may be provided over surfaces of physicalbuttons, trays, flaps, switches, etc. by detecting transmitted signaldisturbances to allow touch input detection without requiring detectionof physical movement/deflection of a component of the device (e.g.,detect finger swiping over a surface of a physical button). In someembodiments, the touch input regions on the sides may be divided intodifferent regions that correspond to different functions. The touchinput provided in region 1540 (and likewise in region 1542) is detectedalong a one-dimensional axis. For example, a touch location is detectedas a position on its lengthwise axis without differentiating the widthof the object touching the sensing region. In an alternative embodiment,the width of the object touching the sensing region is also detected.Regions 1540 and 1542 correspond to regions beneath which touch inputtransmitters and sensors are located. Although two touch input regionson the housing of the device have been shown in FIG. 15A, other touchinput regions on the housing may exist in various other embodiments. Forexample, surfaces on top (e.g., surface on top view 1536) and/or bottom(e.g., surface on bottom view 1538) of the device are touch inputenabled. The shapes of touch input surfaces/regions on device sidewalls(e.g., regions 1540 and 1542) may be at least in part flat, at least inpart curved, at least in part angular, at least in part textured, and/orany combination thereof.

FIG. 15B is a block diagram illustrating an embodiment of a system fordetecting a touch input surface disturbance. In some embodiments, thesystem shown in FIG. 15B is included in the device shown in FIG. 15A.For example, FIG. 15B shows components utilized to detect a touch inputon a sidewall external surface 1540 of FIG. 15A. In some embodiments,the system shown in FIG. 15B is included in a computing device, anentertainment device, a smartphone, a tablet computer, a point of saleterminal, a food and restaurant apparatus, a gaming device, a casinogame and application, a piece of furniture, a vehicle, an industrialapplication, a financial application, a medical device, an appliance,and any other objects or devices having a touch input surface.Propagating signal medium 1502 is coupled to transmitters 1504, 1513,1506, 1516, and 1510 and receivers/sensors 1505, 1508, 1512, 1514, and1518. The locations where transmitters 1504, 1513, 1506, 1516, and 1510and sensors 1505, 1508, 1512, 1514, and 1518 are located with respect topropagating signal medium 1502 and with respect to each other, as shownin FIG. 15B, are merely an example. Likewise, the number of transmittersand receivers need not be equal. In some embodiments, propagating signalmedium 1502 is a part of a housing of a device. For example, thetransmitter and receivers are coupled to a sidewall of a housing of asmartphone device to detect touch inputs on the side of the device. Insome embodiments, the shown portion of propagating signal medium 1502corresponds to touch input region 1540 of FIG. 15A. For example, theshown elongated region of medium 1502 corresponds to a region of a sideof a smartphone device where touch input is able to be provided.

Other configurations of transmitter and sensor locations may exist invarious embodiments. Although FIG. 15B shows alternating transmittersand receivers arranged inline, locations of transmitters and sensors maybe intertwined and spaced and arranged in any configuration in variousother embodiments. The gap between transmitter 1510 and sensor 1512 maycorrespond to a location where a SIM/memory card opening is to belocated. Any number of transmitters and/or sensors may be utilized invarious embodiments. In some embodiments, rather than using a dedicatedtransmitter and a dedicated sensor, a transducer that acts as both atransmitter and a sensor is utilized. In various embodiments, thepropagating medium includes one or more of the following materials:polymer, plastic, wood, steel, metal and any medium that is able topropagate an acoustic or ultrasonic signal. For example, medium 1502 isa portion of a metal sidewall/side-edge of a smartphone or a tabletcomputer device where a user is to hold the device. FIG. 15B only showstransmitters and sensors for one side of a device as an example andanother set of transmitters and sensors may be placed on another side ofthe device to detect inputs on this other side of the device (e.g., alsoconnected to touch detector 1520). Objects of FIG. 15B are not drawn toscale.

Medium 1502 includes a surface area where a user may touch to provide acommand input. In various embodiments, the touch input surface of medium1502 is flat, curved, or combinations thereof. The touch input is to bedetected along a lengthwise region (e.g., locations in the region to beonly identified along a one-dimensional axis). A one-dimensionallocation and a force of a touch input along an external sidewall surfaceof the device may be detected without actuation of a physical button oruse of any other sensor that requires a physical deflection/movement ofa component of the device. For example, a user provides an input on theexternal surface of medium 1502 that covers the shown transmitters andreceivers that are mounted on an opposite internal surface/side ofmedium 1502 (e.g., mounted on an internal side of device sidewall insidea device and the touch input is provided on the other side of the devicesidewall that is the external surface of the device sidewall) and theinput disturbs a transmitted signal traveling within medium 1502 (e.g.,by at least one of the shown transmitters) that is detected (e.g., by atleast one of the shown sensors) and analyzed to identify a location onthe external surface of medium 1502 where the input was provided. Thisallows virtual buttons to be provided on a smooth side surface and anindication of a virtual button press is detected when a user appliespressure of sufficient force at a specific location of a virtual buttonon the side surface region. In some embodiments, a length of the axiswhere a touch input is able to be detected starts from an externalsurface over a mounting location of transmitter 1504 to an externalsurface over a mounting location of sensor 1518.

Examples of transmitters 1504, 1506, 1510, 1513, and 1516 includepiezoelectric transducers, piezoresistive elements/transmitters,electromagnetic transducers, transmitters, sensors, and/or any othertransmitters and transducers capable of propagating a signal throughmedium 1502. Examples of sensors 1505, 1508, 1512, 1514, and 1518include piezoelectric transducers, piezoresistive sensors/receivers,electromagnetic transducers, laser vibrometer transmitters, and/or anyother sensors and transducers capable of detecting a signal on medium1502. Although five transmitters and five sensors are shown, any numberof transmitters and any number of sensors may be used in otherembodiments. In the example shown, transmitters 1504, 1506, 1510, 1513,and 1516 each may propagate a signal through medium 1502. A signalemitted by a transmitter is distinguishable from another signal emittedby another transmitter. In order to distinguish the signals, a phase ofthe signals (e.g., code division multiplexing), a frequency range of thesignals (e.g., frequency division multiplexing), or a timing of thesignals (e.g., time division multiplexing) may be varied. One or more ofsensors 1505, 1508, 1512, 1514, and 1518 receive the propagated signals.

Touch detector 1520 (e.g., included and mounted on an internal circuitboard) is connected to at least the transmitters and sensors shown inFIG. 15B. In some embodiments, detector 1520 includes one or more of thefollowing: an integrated circuit chip, a printed circuit board, aprocessor, and other electrical components and connectors. Detector 1520determines and sends signals to be propagated by transmitters 1504,1506, 1510, 1513, and 1516. Detector 1520 also receives the signalsdetected by sensors 1505, 1508, 1512, 1514, and 1518. The receivedsignals are processed by detector 1520 to determine whether adisturbance associated with a user input has been detected at a locationon a surface of medium 1502 associated with the disturbance. Detector1520 is in communication with application system 1522. Applicationsystem 1522 uses information provided by detector 1520. For example,application system 1522 receives from detector 1520 a locationidentifier and a force identifier associated with a user touch inputthat is used by application system 1522 to control configuration,setting or function of a device, operating system and/or application ofapplication system 1522. For example, a user indication to increasevolume is detected when a touch input of sufficient pressure is detectedwithin one range of locations along a one-dimensional axis, while a userindication to decrease volume is detected when an input of sufficientpressure is detected within another range of locations. Such regions canbe fixed, or can be defined in software. For example, a right-handeduser could have a region to change volume assigned to the detectionregion on the left side of the case, whereas a left-handed user couldreverse this assignment.

In some embodiments, application system 1522 includes a processor and/ormemory/storage. In other embodiments, detector 1520 and applicationsystem 1522 are at least in part included/processed in a singleprocessor. An example of data provided by detector 1520 to applicationsystem 1522 includes one or more of the following associated with a userindication: a location coordinate along a one-dimensional axis, agesture, simultaneous user indications (e.g., multi-touch input), atime, a status, a direction, a velocity, a force magnitude, a proximitymagnitude, a pressure, a size, and other measurable or derivedinformation.

FIG. 15C is a diagram illustrating an embodiment of a device housingwith touch input enabled sides. Housing 1552 shows a unibody back andside housing of an electronic device. For example, housing 1552 may beutilized as a part of a housing for a smartphone device that houseselectrical components and is covered with a display glass surface.Transmitters 1504, 1506, 1510, 1513, and 1516 and sensors 1505, 1508,1512, 1514, and 1518 (also shown in FIG. 15B) have been mounted on aninternal side/surface of a sidewall (e.g., sidewall internalsurface/side facing inside the electronic device) of housing 1552.Housing 1552 may be made of metal (e.g., aluminum), plastics, ceramics,carbon fiber, or any other material of propagating medium 1502 of FIG.15B. The transmitters and sensors are mounted on flex cable 1554. Flexcable 1554 includes patterned conductors that connect the transmittersand sensors/receivers to pins on connector 1556. In some embodiments,connector 1556 connects to a circuit board (not shown) that includes atouch detector (e.g., touch detector 1520) that provides/receivessignals to/from the transmitters/receivers. The transmitters andsensors/receivers of flex cable 1554 are utilized to detect touch inputon an external side surface of housing 1552 over the region directlyabove and between the transmitters and sensors/receivers of flex cable1554 (e.g., to detect location and force along a one-dimensional axisidentifying lengthwise locations on the external side surface). Thisallows the side surface of housing 1552 to be touch sensitive to userinputs. Although housing 1552 does not show any physical buttons in thetouch input surface, in various other embodiments, one or more physicalbuttons may exist. For example, touch input detection may be provided ona surface of a physical button (e.g., transmitter/sensor mountedbehind/around a physical button) to allow a user to provide a touchindication over a surface of a physical button without physicallyactuating the physical button (e.g., detect swipe gesture over physicalbutton).

Much like flex cable 1554, flex cable 1558 connects transmitters andsensors mounted on a second internal surface/side of a second sidewall(e.g., sidewall internal surface/side facing inside cavity of theelectronic device) to connector 1560 (e.g., connects to the circuitboard that includes touch detector 1520 of FIG. 15B). The transmittersand sensors/receivers of flex cable 1558 are utilized to detect touchinput on external side surface 1562 of housing 1552 over the regiondirectly above and between the transmitters and sensors/receivers offlex cable 1558. This allows sidewall surface 1562 to be touch sensitiveto user inputs. In various embodiments, other transmitters andsensors/receivers may be mounted on other internal walls and surfaces ofhousing 1552 to allow touch inputs on other external surfaces of housing1552.

Although the shown transmitters and sensors/receivers have been directlymounted on flex cable 1554 in a straight line along a strip/bar of flexcable 1554, the sensors/receivers and transmitters may be mounted on aflex cable in various other embodiments. For example, FIG. 15E showstransmitters and receivers mounted on fingers of flex cable 1564. Thismay allow flexibility in routing the flex cable around other internalcomponents of a device. For example, the fingers allow the flex cable tobe routed around openings and components to accommodate a switch,button, SIM/memory card tray, etc.

When manufacturing the configuration shown in FIG. 15C, it may beinefficient to individually attach each individual transmitter/sensoronto a flex cable. In some embodiments, transmitters and sensors arepositioned/placed on a stiffener bar (e.g., mounting template bar) thatassists in the positioning and alignment of the transmitters and sensorsand all of the transmitters and sensors on the stiffener bar areattached to a flex cable together at the same time using the stiffenerbar. Once transmitters/sensors are attached to the flex cable, each ofthe transmitters/sensors on the flex cable are attached to thepropagating medium/housing via an adhesive (e.g., epoxy). Thetransmitters and sensors shown in the example of FIG. 15C have beenplaced inside cavities/pockets etched on the internal side/surface ofsidewall of housing 1552. FIG. 15D shows a magnified view of thecavity/pocket (e.g., 0.3 millimeter in depth). By placing eachtransmitter/sensor in the cavity, valuable internal space inside thehousing is maintained and the flex cable assembly with the transmittersand receivers is able to be mounted flush to the sidewall.

FIGS. 15F-15H show different embodiments of transmitter and sensorcomponent arrangements utilized to detect a touch input along a lineararea (e.g., transmitters and sensors mounted inside of a device on aninternal surface of sidewall to detect touch input on an externalsurface of the sidewall). For example, FIGS. 15F-15H show alternativearrangements of at least a portion of the transmitters and sensors shownin FIGS. 15B and 15E. In various embodiments, at least a portion of thetransmitter and sensor components shown in FIGS. 15F-15H are connectedto touch detector 1520 shown in FIG. 15B. For example, rather than usingthe arrangement of transmitters and sensors shown in FIG. 15B, thearrangement shown in FIG. 15F, 15G, or 15H is utilized. Examplecomponents of touch detector 1520 are components included in touchdetector 802 of FIG. 8. Connections between transmitter and sensorcomponents in FIGS. 15F-15H and touch detector 1520 have not been shownin FIGS. 15F-15H. Other components (e.g., application system 1522)connected to touch detector 1520 also have not been shown in FIGS.15F-15H. Components are not drawn to scale. A piezoelectric transmitteris shown as a box labeled with a “T.” A piezoelectric sensor is shown asa box labeled with an “S.” A piezoresistive sensor is shown as a circlelabeled with an “S.” In some embodiments, the shown piezoelectrictransmitters and sensors are coupled to an inside surface border of aglass cover of a touchscreen display. In some embodiments, the shownpiezoresistive sensors are coupled behind a display panel (e.g., behindLED/OLED panel). The number of transmitters and sensors shown in FIGS.15F-15H are merely an example and any number of any type of transmittersand sensors may exist in various embodiments.

In some embodiments, a device includes one or more piezoelectrictransmitters and one or more piezoelectric receivers/sensors to detect atouch input location (e.g., coupled to glass of touch screen, coupled toside of metal housing of a device to detect touch input location ondevice side, etc.) as well as an array of piezoresistive sensors todetect touch input force/pressure (e.g., array of piezoresistive sensorscoupled behind LED/OLED display panel to detect magnitude of deformationof the panel due to touch input, or one or more piezoresistive sensorscoupled to inside of a device housing to detect grip force, etc.).Transmitter and sensor arrangement 1582 shown in FIG. 15F includespiezoelectric transmitters/sensors around a border area of apropagating/touch input medium and an array of piezoresistive sensors.

In some embodiments, given the increased piezoresistive sensorsensitivity using the improvements described herein, one or morepiezoresistive sensors are utilized to receive/detect propagatedultrasonic touch input medium signals for touch input locationdetection. The same piezoresistive sensors may also be used to detectphysical disturbance magnitude as well. For example, an output signalfrom the piezoresistive sensor is first analyzed and correlated with itsinput supply voltage signal to detect the physical disturbance magnitude(e.g., using the process of FIG. 6) and then when the propagatedultrasonic signal is detected after propagation through the touch inputmedium, the output signal (e.g., delayed signal) from the piezoresistivesensor is analyzed and correlated with an expected baseline propagatedsignal to detect a propagation delay caused by the touch input indetermining the associated touch input location (e.g., using the processof FIG. 10 and/or FIG. 16). Thus the same output signal from apiezoresistive sensor can be used to both detect touch force and touchlocation (e.g., by the same signal processing component: touch detector1520). Example sensor configurations for devices including piezoelectrictransmitters and piezoresistive sensors without piezoelectric sensorsare shown in arrangement 1584 of FIG. 15G.

In some embodiments, piezoresistive sensors are utilized to detect atouch input location without a use of piezoelectric transmitters. Forexample, given an array of piezoresistive sensors, a location of a touchinput is triangulated based on the detected physical disturbancemagnitudes and the relative locations of the sensors that detected thevarious magnitudes (e.g., using a matched filter). Example sensorconfigurations for devices including piezoresistive sensors withoutpiezoelectric transmitters are shown in arrangement 1586 of FIG. 15H.

In some embodiments, data from piezoelectric transmitters/sensors anddata from piezoresistive sensors are used to complement and augment eachother. A touch input location information detected using piezoelectrictransmitters/sensors may be used to cross qualify physical disturbancemagnitude information from piezoresistive sensors. For example, when itis detected (using piezoresistive sensor data) that touch input is beingprovided with low force, pressure, strain, etc. (e.g., user is wearing aglove that absorbs force), a piezoelectric transmitter gain and/orsensor sensitivity is increased to enable better touch input locationdetection. In another example, if a sufficient physical disturbancemagnitude is detected but a touch input location is not detected (ortouch input location is detected in a specific signature pattern), thenit may be concluded that the detected input is a result of devicebending (e.g., in a pocket) rather than as a result of an intended userinteraction.

FIG. 16 is a flowchart illustrating an embodiment of a process to detecta touch input. The process of FIG. 16 may be performed by touch detector1520 connected to an arrangement of transmitters and sensors shown inFIGS. 15B-15H. In one example of a system which performs the process ofFIG. 16, the first transmitter, the second transmitter, and the receiverare embedded in the side of a phone. A touch and/or force sensor (e.g.,implemented on some type of processor, such as an application-specificintegrated circuit (ASIC), a field-programmable gate array (FPGA), or ageneral purpose processor) in the phone inputs a received signal whichis output by the receiver and includes propagating signals from thetransmitters. The touch and/or force sensor analyzes the received signalto identify touches and/or estimate a force value for any identifiedtouches.

At 1670, a first transmitter is used to transmit a first propagatingsignal to a receiver through a propagating medium, wherein the firstpropagating signal propagates through a first region of the touch inputmedium corresponding to a first signal path through the touch inputmedium between the first transmitter and the receiver. As will bedescribed in more detail below, in some embodiments, transmitters andreceivers exchange acoustic or ultrasonic signals. In some embodiments,the propagating medium is substantially linear or one-dimensional, andthe transmitters and receivers are arranged in a line within the 1Dpropagating medium (e.g., along the side of a phone).

At 1672, a second transmitter is used to transmit a second propagatingsignal, different from the first propagating signal, to the receiverthrough the propagating medium, wherein the second propagating signalpropagates through a second region of the touch input mediumcorresponding to a second signal path through the touch input mediumbetween the second transmitter and the receiver and the second region isa subset of the first region. For example, the second transmitter maysit between the first transmitter and the receiver in a line, such thatthe second region (e.g., through which the second propagating signalpropagates) is a subset of the first region (e.g., through which thefirst propagating signal propagates).

At 1674, at least the first propagating signal and the secondpropagating signal are analyzed to identify, based on a determinationthat the first signal path was disturbed by a touch input while thesecond signal path was not disturbed by the touch input, the touch inputon a part of the first region that is not part of the second region. Aswill be described in more detail below, if the first signal passesthrough the touch input while the second signal does not (e.g., wherethe touch or lack thereof is indicated by the amplitude of the signals),that is indicative of a touch in the part of the first region which isnot part of the second region.

It is noted that the process of FIG. 16 not only identifies when a touchhas occurred, but the location of that touch is also determined orotherwise identified. For example, since the positions of the varioustransmitters and receivers are known, the presence of a touch betweentwo adjacent transmitters and/or receivers corresponds to knowing theposition of that touch (e.g., where that touch occurs on the side of asmartphone or tablet). In some embodiments, the process of FIG. 16identifies multiple touch inputs which occur simultaneously on theinteractive surface (e.g., so that the locations of multiple touchesis/are identified). This is desirable because applications which requiremultiple, simultaneous touch inputs can be supported.

In some embodiments, a force value is determined for each detected oridentified touch. For example, if a sensor identifies two touches, thesensor may also estimate a force value for each identified touch (e.g.,where the two force values are permitted to be different values).

The following figure shows an example of two transmitters and a receiverwhich are embedded in the side of a phone and which exchange the signalsdescribed and/or used above.

FIG. 17 is a diagram illustrating an embodiment of a receiver and twoassociated transmitters in the side of a phone. In this example, theexemplary phone (1702) has multiple interactive surfaces, including thefront surface (1704) and the side surface (1706). For example, havingthe side of the phone be interactive or touch-sensitive may permit theuser to use the side of the phone as a scroll bar or for volume control.Although not shown here, in some embodiments, the other side surface(e.g., opposite to surface 1706) is also an interactive surface.

In this example, the transmitters and receivers are configured toexchange an acoustic or ultrasonic signal. Such signals may be desirablebecause they work well in a variety of propagating mediums, includingones that have not worked well with previous touch and/or force sensingtechniques. For example, the sides of some phones are made of metal,which does not work well with existing touch and/or force sensors whichrely upon capacitors (e.g., because of the stiffness of the metal and/orthe conductive properties of the metal). In contrast, acoustic orultrasonic signals can propagate through metal relatively easily. Insome embodiments, piezoelectric transducers are used for thetransmitters and/or receivers. In some embodiments, piezoresistivetransducers are used for the transmitters and/or receivers.

Diagram 1700 shows the system when the side of the phone is not beingtouched. The side of the phone (1706) includes from left to right: afirst transmitter (1708), a second transmitter (1710), and a receiver(1712). (To preserve the readability of this diagram, other transmittersand receivers are not shown but naturally additional transmitters and/orreceivers may be included.) In diagram 1700, the transmitted signalspropagate through different paths along the side of the phone. The firstsignal (1714 a) travels through a first region (e.g., shown as dottedregion 1718) between the first transmitter and the receiver. The secondsignal (1716 a) travels through a second region (e.g., shown as shadedregion 1720). Region 1718 and region 1720 show some examples of a firstregion and a second region which are referred to in the process of FIG.16.

Diagram 1750 shows the phone when a single touch (1752) is applied tothe side of the phone. For readability, the first region (shown indiagram 1700 as dotted region 1718) and the second region (shown indiagram 1700 as shaded region 1720) are not shown in diagram 1750. Inthis example, the touch is located between the first transmitter (1708)and the second transmitter (1710). This is an example of the touchscenario referred to at step 1674 in FIG. 16.

Touch 1752 causes the first signal (1714 b) to be absorbed to somedegree. In this example, the absorption is observable in the amplitudeof the signal where the amplitude of a signal where there is no touch isgreater than if the signal passed through the touch. In one example ofhow step 1674 in FIG. 16 is performed, a touch input (e.g.,corresponding to touch 1752) is identified between the first transmitter(1708) and the second transmitter (1710) if the amplitude of signal 1714b decreases compared to some (e.g., first) reference amplitude, but theamplitude of signal 1716 b remains the same compared to some (e.g.,second) reference. To summarize:

TABLE 1 Amplitude change(s) when going from the untouched state shown indiagram 1700 to the touched state shown in diagram 1750 in FIG. 17.First Signal from T₁ Second Signal from T₂ Conclusion Amplitudedecreases Amplitude is the same A touch input between compared to acompared to a T₁ and second previous/reference previous/referencetransmitter is present amplitude amplitude

In some embodiments, the term amplitude refers to the absolute value ofa peak (e.g., a minimum or maximum) associated with a signal. In someembodiments, the absolute value of the peak is determined after somepre-processing (e.g., to remove less desirable contributions to thereceived signal).

In some cases, the system may go from the state shown in diagram 1750 tothe state shown in diagram 1700. In one special case, this may occur ifthe phone is powered on and the system performs an initializationprocess with touch 1752 applied (e.g., as shown in diagram 1750) andthen the user subsequently removes his/her finger from the interactivesurface. Independent of whether that transition occurs during aninitialization process:

TABLE 2 Amplitude change(s) when going from the touched state shown indiagram 1750 to the untouched state shown in diagram 1700 in FIG. 17.First Signal from T₁ Second Signal from T₂ Conclusion Amplitudeincreases Amplitude is the same A touch input between compared to acompared to a T₁ and second previous/reference previous/referencetransmitter is no longer amplitude amplitude there

As the above shows, when a touch sensor detects that the amplitude ofthe first signal increases and the amplitude of the second signalremains the same (e.g., compared to some reference amplitude(s)), insome embodiments the touch sensor indicates that a touch (e.g., whichwas present or identified before) is no longer present between the firstand second transmitter.

The above table demonstrates a benefit to the sensor embodimentsdescribed herein. Some existing touch sensors in phones have problemswhen the phone is powered on with a user touching an interactivesurface. When this occurs and the initialization process of the touchsensor runs, the sensor is initialized with settings or informationassociated with the phone being touched. This is undesirable becausewith that initialization, the capacitive touch sensors cannot detectwhen the phone is no longer being touched and/or complex processes mustbe performed in order to correct this. In contrast, because there is anobservable change in the amplitude of the signal when a touch leaves, itis easier for the sensors described herein to detect when an interactivesurface goes from a touched state to an untouched state by looking atthe amplitude of the signal(s) (e.g., even if the system initializes ina touched state).

In this example, each transmitter transmits its signal in a manner thatis orthogonal to the other transmitters. For example, the firsttransmitter may use a first pseudo-random binary sequence (PRBS) totransmit its signal and the second transmitter may use a second,different PRBS which creates orthogonality between the transmittersand/or transmitted signals. Such orthogonality permits a processor orsensor coupled to the receiver to filter for or otherwise isolate adesired signal from a desired transmitter.

In some embodiments, the different transmitters use time-shiftedversions of the same PRBS. For example, at the receiver, the receivedsignal (e.g., which is a combination of the different transmittedsignals from the various transmitters) is correlated against thetransmitted signal. Generally speaking, the received signal iscorrelated against the transmitted one. The signal to transmit isselected for its good auto-correlation properties, that is,auto-correlation must be strong at offset 0 and very low everywhereelse. After correlation, the resulting signal has multiple sharp peakswhere each peak corresponds to a different transmitter (e.g., becausethe different starting points or phases of the time-shiftedpseudo-random bit sequences result in different offsets or locations ofthe peaks). For example, in this scenario where there are twotransmitters, one peak in the correlated signal corresponds to thesignal from the first transmitter and a second peak (e.g., at adifferent offset or location compared to the first peak) corresponds tothe signal from the second transmitter. In some embodiments, usingtime-shifted versions of the same PRBS is desirable becauseauto-correlation of a PRBS has a very strong peak at offset 0 and isrelatively small everywhere else. The correlation of two different PRBSsequences is not so small. Time shifting the same PRBS for eachtransmitter provides the lowest correlation between transmitters (atleast for a portion of the whole sequence).

In some embodiments, the transmitters use orthogonal codes to createorthogonality between the transmitted signals (e.g., in addition to oras an alternative to creating orthogonality using a PRBS). In variousembodiments, any appropriate technique to create orthogonality may beused.

In at least some cases, the system may not be able to detect if twotouches occur between the first transmitter (1708) and the secondtransmitter (1710). For this reason, in some embodiments, transmittersand receivers are spaced relatively close together, for example, lessthan the width of an expected touch. In one example, the transmittersand receivers are spaced ˜10 mm apart. If the transmitters and receiversare spaced relatively close to each other, then the likelihood ofmultiple touches occurring between adjacent transmitters and/orreceivers is reduced, and/or if multiple touches did occur so closetogether but were not identified it would be acceptable (e.g., from auser experience point of view).

One benefit to the shared sensor embodiments described herein (e.g.,where a given receiver listens for or to multiple transmitters) is thatthe number of receivers is reduced. For example, in a non-sharedreceiver layout there is a 1:1 ratio of transmitters and receivers andmore receivers would be required (e.g., compared to a shared receiverembodiment) in order to achieve the same density of transmitters and/orreceivers. Having more receivers is undesirable because of the routingrequirements associated with each receiver. Suppose (for simplicity)there is a single chip which performs touch and/or force sensing. Theoutput from each of the receivers needs to be routed to the sensor chip.Therefore, more receivers require more routing which consumes more space(e.g., on some printed circuit board or within the phone itself ingeneral) and/or costs more money. For this reason, a shared receiverconfiguration (one example of which is shown here) is attractive.

The following figures describe the above tables more formally inflowcharts.

FIG. 18 is a flowchart illustrating an embodiment of a process toidentify a touch input in a part of a first region that is not part of asecond region using signal amplitudes. FIG. 18 corresponds to Table 1and a transition from diagram 1700 to diagram 1750 in FIG. 17. In someembodiments, the process is used at step 1674 in FIG. 16.

At 1800, the amplitude of the first propagating signal is comparedagainst a reference amplitude associated with the first propagatingsignal. For example, in FIG. 17, the amplitude of signal 1714 a (e.g.,where there is no touch) is an example of a saved and/or referenceamplitude of the first propagating signal and signal 1714 b (e.g., wherethere is a touch) is an example of an (e.g., current) amplitude of thefirst propagating signal.

At 1802, the amplitude of the second propagating signal is comparedagainst a reference amplitude associated with the second propagatingsignal. For example, in FIG. 17, the amplitude of signal 1716 a is anexample of a saved and/or reference amplitude of the second propagatingsignal and signal 1716 b is an example of an (e.g., current) amplitudeof the second propagating signal.

It is noted that the first signal and the second signal use differentreferences at step 1800 and step 1802. In some embodiments, this isdesirable because it permits different signal paths or parts of the sideof a phone (as an example) to have different reference amplitudes. Forexample, the receivers may be implemented using piezo transducers whichare very sensitive to temperature. If there is some localized “hot spot”along the side of the phone, then it would be desirable to have onereference amplitude for signals which pass through the hot spot and adifferent reference amplitude for signals which do not pass through thehot spot. In other words, using different reference amplitudes maypermit the sensor to more accurately detect a touch and/or moreaccurately estimate a force value. In some embodiments, for eachtransmitter-receiver pair there is stored a reference signal (e.g., fromwhich the reference amplitude is obtained) or just the referenceamplitude itself (e.g., if no other information from the referencesignal is desired).

At 1804, in the event: (1) the amplitude of the first propagating signalhas decreased compared to the reference amplitude associated with thefirst propagating signal and (2) the amplitude of the second propagatingsignal remains substantially the same compared to the referenceamplitude associated with the second propagating signal, (A) the part ofthe first region that is not part of the second region is included inthe touch input and (B) the second region is excluded from the touchinput. For example, in FIG. 17, touch 1752 causes the amplitude of thefirst signal (1714 a/1714 b) to decrease whereas the amplitude of thesecond signal (1716 a/1716 b) does not change. A touch is thereforeidentified in that part of the first region which is not part of thesecond region (e.g., between the first transmitter (1708) and secondtransmitter (1710)), but the identified touch does not include thesecond region (e.g., between the second transmitter (1710) and thereceiver (1712)).

FIG. 19 is a flowchart illustrating an embodiment of a process toidentify when a touch input leaves a part of a first region that is notpart of a second region using signal amplitudes. FIG. 19 corresponds toTable 2 and a transition from diagram 1750 to diagram 1700 in FIG. 17.In some embodiments, the process of FIG. 19 is performed in combinationwith FIG. 16 and/or FIG. 18 (e.g., the process of FIG. 16 and/or FIG. 18detects when there is a touch and the process of FIG. 19 detects whenthat touch goes away).

At 1900, the amplitude of the first propagating signal is comparedagainst a reference amplitude associated with the first propagatingsignal. At 1902, the amplitude of the second propagating signal iscompared against a reference amplitude associated with the secondpropagating signal.

For example, in FIG. 17, diagram 1700 shows an exemplary previous stateof the system and diagram 1750 shows an exemplary current state of thesystem. The amplitudes associated with the signals in diagram 1700 aretherefore examples of previous and/or reference amplitudes and theamplitudes associated with the signals in diagram 1750 are examples of(e.g., current) amplitudes.

At 1904, in the event: (1) the amplitude of the first propagating signalhas increased compared to the reference amplitude associated with thefirst propagating signal and (2) the amplitude of the second propagatingsignal remains substantially the same compared to the referenceamplitude associated with the second propagating signal, it is indicatedthe touch input is no longer present in the part of the first regionthat is not part of the second region. As described above, if theamplitude of the first signal goes up and the amplitude of the secondsignal remains the same, this is indicative of a touch leaving that partof the first region which does not include the second region (e.g.,between the first transmitter (1708) and the second transmitter (1710)in FIG. 17).

The following figure describes using time-shifted versions of the samePRBS more formally in a flowchart.

FIG. 20 is a flowchart illustrating an embodiment of a process to usetime-shifted versions of the same PRBS when transmitting. At 2000, thefirst propagating signal is transmitted using a pseudo-random binarysequence. In some embodiments, step 1670 in FIG. 16 includes step 2000.

At 2002, the second propagating signal is transmitted using atime-shifted version of the pseudo-random binary sequence used totransmit the first propagating signal. In some embodiments, step 1672 inFIG. 16 includes step 2002.

At 2004, the receiver is used to obtain a received signal which includesthe first propagating signal and the second propagating signal.

At 2006, the received signal is correlated with the transmitted signal.As described above, the time-shifting causes the first propagatingsignal and second propagating signal to be separated out in the outputof the correlator (e.g., one peak in the correlation signal correspondsto the first propagating signal and another peak in the correlationsignal corresponds to the second propagating signal). In someembodiments, step 1674 in FIG. 16 includes step 2006. In someembodiments, correlation is performed before the (e.g., current or new)amplitude of the signal is compared to some reference amplitude.

The following figure shows a more detailed example of how touchdetection and force estimation are performed on the side of a phone withmore signals contributing to processing.

FIG. 21 is a diagram illustrating an embodiment of a side of a phonewith multiple transmitters and multiple receivers. Diagram 2100 showsthe exemplary transmitters and receivers laid out along the side of aphone. In this example, each receiver is associated with and listens tosome number of transmitters. Group 2102 shows the transmitters that thefirst receiver (2104) listens for, group 2106 shows the transmittersthat the second receiver (2108) listens for, group 2110 shows thetransmitters that the third receiver (2112) listens for, and group 2116shows the transmitters that the fourth receiver (2114) listens for.

In this example, transmitters with the same index use the sametime-shifted PRBS to transmit their signal. That is, all firsttransmitters use a PRBS with a first time shift, all second transmittersthe same PRBS but with a second time shift, and so on. To ensure thatonly the appropriate signals from the appropriate transmitters areanalyzed downstream, in some embodiments, filtering (e.g., based onpropagation time) is performed so that signals from more distanttransmitters (e.g., which are not part of a receiver's group) areignored.

Diagram 2150 shows an example of the filtering performed. For clarityand ease of explanation, suppose that all of the transmitters transmitat time 0. The propagation medium and its properties are known ahead oftime (e.g., it is known that the side of a phone will be made of metal)and so the propagation time of a signal from a given transmitter to agiven receiver is known. As used herein, t_(Δ) is the propagation timeof a signal from a transmitter to an adjacent receiver (e.g., from T₃(2118) to second receiver (2108)). Similarly, t_(2Δ) is the propagationtime of a signal from a transmitter to a receiver which is two places orspots away (e.g., from second transmitter (2120) to second receiver(2108)).

Again for clarity and ease of explanation, the transmission signals(2152 and 2154) in this example are represented as relatively shortpulses; note that they occur or otherwise arrive at time t_(Δ) andt_(2Δ). Given the propagation times described above, the transmission(2152) from an adjacent transmitter (e.g., from T₃ (2118) to secondreceiver (2108)) arrives at the receiver at time t_(Δ). The transmission(2154) from a transmitter two spots away arrives at the receiver at timet_(2Δ) (e.g., from second transmitter (2120) to second receiver (2108)).

As shown in diagram 2150, filtering (2156) is performed from time 0 totime (t_(Δ)−margin). Filtering (2158) is also performed from time(t_(2Δ)+margin) onwards. This causes any signal received before(t_(Δ)−margin) or after (t_(2Δ)+margin) to be ignored. As a result, onlysignals which are receive between t_(Δ) (minus some margin) and t_(2Δ)(plus some margin) are further analyzed and/or processed by downstreamprocessing.

This filtering helps to prevent a transmission from a distanttransmitter (e.g., which is not part of a receiver's group) from beinganalyzed. For example, this filtering may prevent third receiver (2112)from passing along (e.g., to a downstream process) the transmittedsignal of second transmitter (2120), which is not in that receiver'sgroup. It may also prevent a receiver from passing on (e.g., to adownstream process) a reflected signal which is reflected off the edgeof the propagation medium. Generally speaking, filtering helps toprevent the introduction of noise which improves the quality of thesensing and/or simplifies the signal processing.

The following figure describes the filtering shown here more formally ina flowchart.

FIG. 22 is a flowchart illustrating an embodiment of a process to filtera received signal. In some embodiments, the process of FIG. 22 isperformed in combination with the process of FIG. 16. For example,filtering may be performed first before the process of FIG. 16 and thefiltered signal is subsequently analyzed (e.g., at step 1674 in FIG.16).

At 2200, the receiver is used to obtain a received signal which includesthe first propagating signal and the second propagating signal, wherein:(1) the first propagating signal is associated with a first propagationtime through the propagating medium from the first transmitter to thereceiver and (2) the second propagating signal is associated with asecond propagation time through the propagating medium from the secondtransmitter to the receiver. For example, in FIG. 21, receiver 2108receives a signal from the second transmitter (2120) which takes t_(2Δ)units of time to propagate through the side of the phone and receives asignal from the third transmitter (2118) which takes t_(Δ) units of timeto propagate through the side of the phone. Note that the receivedsignal (e.g., before filtering) includes reflections from the end of thepropagation medium and/or transmissions from transmitters which are notpart of that receiver's group.

At 2202, filtering is performed on the received signal in order toobtain a filtered signal, wherein the filtered signal includes at least:(1) a part of the received signal which corresponds to the firstpropagation time and (2) a part of the received signal which correspondsto the second propagation time. See, for example, FIG. 21 where parts ofthe received signal before (t_(Δ)−margin) and after (t_(2Δ)+margin) arefiltered out but the desired transmission signals 2152 and 2154 arestill included after filtering. Any appropriate type of filter may beused.

It is noted that the order of transmitter and receiver indices does notfollow the same pattern throughout the sample shown. For example, on theleft hand side, the order is T₂ (2120), T₃ (2118) whereas in the middleit's T₃ (2126) and then T₂ (2128). This is intentional so that (as anexample) R₃ (2112) hears from both a T₂ on its left (2120) and a T₂ onits right (2128). To separate them in the correlated signal, the T₂ onthe left is placed as far as possible from R₃. The same logic applies toR₂ (2108) and the T₂ on its left (2120) and the T₂ on its right (2128).

Returning to FIG. 21, the following describes an example in which atouch is detected and a force value is determined by determining a valueor metric for each gap between adjacent transmitters and/or receivers.In this example, touch 2122 is detected and a force value is determinedfor touch 2122.

In diagram 2100, x₁ corresponds to the gap between the first transmitter(2124) and the first receiver (2104), x₂ corresponds to the gap betweenthe first receiver (2104) and the second transmitter (2120), and so on.In this example, the value calculated for gap x₁ is:x ₁ =T ₁ R ₁where (generally speaking) T_(i)R_(j) is a metric or value associatedwith a degree of change (if any) of an (e.g., current or new) amplitudecompared to some reference amplitude. More specifically:

${T_{i}R_{j}} = {10\log_{10}{\frac{{Amplitude}_{{new}\;}}{{Amplitude}_{reference}}.}}$In some embodiments, each transmitter-receiver pair has its ownamplitude reference value. For example, as described above, there may besome localized hot spot which causes the transmitters and/or receiversin one part of the transmission medium to behave differently than inanother part of the transmission medium and this difference should betaken into account when calculating the amplitude metrics.

The following figure shows an example of how the values which are inputinto the T_(i)R_(j) calculation shown above may be obtained.

FIG. 23 is a diagram illustrating an embodiment of a signal afterpassing through different types of touches, if any. In some embodiments,the signals shown are envelopes, where some underlying signal oscillatesat a frequency much faster than the frequency with which the envelopeschange (e.g., the peaks of the underlying signal define the envelope).In some embodiments, the signals shown are after correlation.

In the example shown, signal 2300 is an example of a signal where thereis no touch and therefore the signal is not absorbed by the touch.Signal 2302, with a lower amplitude than signal 2300, corresponds to asignal where there is a light touch which absorbs the signal. Signal2304, with a lower amplitude than signal 2302, corresponds to a signalwhere there is a heavier touch. That is, more force is applied withsignal 2304 than with signal 2302.

As shown here, as more force is applied, the (peak) amplitude of asignal which passes through that touch decreases correspondingly. In theT_(i)R_(j) equation above, the amplitudereference input is obtained fromthe peak (e.g., global maximum or global minimum) value of a referenceand/or untouched signal, such as signal 2300. For simplicity, thesignals shown here are in the positive domain, but a (e.g., global)minima which is in the negative domain would be used after taking theabsolute value.

The amplitude_(new) input to the T_(i)R_(j) equation above is obtainedsimilarly. For example, if signal 2302 were being processed, the valueamplitude_(light) would be used and if signal 2304 were being processed,the value amplitude_(heavy) would be used. As described above, if thepeak of the signal is negative, then taking the absolute value wouldmake it positive.

Returning to FIG. 5, equations for some other gaps are:

$x_{2} = {{\frac{1}{2}\left( {{T_{2}R_{1}} + \left( {{T_{3}R_{1}} - \left( {{T_{2}R_{2}} - {T_{3}R_{2}}} \right)} \right)} \right)} = {\frac{1}{2}\left( {{T_{2}R_{1}} + {T_{3}R_{1}} - {T_{2}R_{2}} + {T_{3}R_{2}}} \right)}}$$\mspace{20mu}{x_{3} = {\frac{1}{2}\left( {\left( {{T_{2}R_{2}} - {T_{3}R_{2}}} \right) + \left( {{T_{3}R_{1}} - {T_{2}R_{1}}} \right)} \right)}}$$x_{4} = {{\frac{1}{2}\left( {{T_{3}R_{2}} + \left( {{T_{2}R_{2}} - \left( {{T_{3}R_{1}} - {T_{2}R_{1}}} \right)} \right)} \right)} = {\frac{1}{2}\left( {{T_{3}R_{2}} + {T_{2}R_{2}} - {T_{3}R_{1}} + {T_{2}R_{1}}} \right)}}$  ⋮where T_(i)R_(j) is calculated as described above. These values (i.e.,x₁, x₂, x₃, etc.) are sometimes referred to herein as amplitude metrics.

It is noted that the above equations are one example of a way to solvethe problem of converting measurements {T_(i)R_(j)} to segment values{x_(k)}. In some embodiments, some other equations are used. Forexample, different weights can provide other unbiased solutions, perhapswith different statistical variances. For example:x ₂=¾T ₂ R ₁+¼T ₃ R ₁−¼T ₂ R ₂+¼T ₃ R ₂.

It may be useful to discuss the x₃ equation in more detail in order toobtain insight into how the x₂ and x₄ equations are obtained. The twosignals which pass through the x₃ gap are the T₂R₂ signal and the T₃R₁signal. Therefore, it makes sense to use those signals in calculating ametric or value for x₃. However, both of those signals are two-gapsignals but only the x₃ gap is of interest. Therefore, some part ofthose signals should be discounted or otherwise removed. For the T₂R₂signal, this can be done by subtracting out T₃R₂, since that signal is aone-gap signal and exactly matches the part of the T₂R₂ signal which istrying to be removed or discounted. This produces the (T₂R₂−T₃R₂) partof the x₃ equation above. Similarly, the T₂R₁ signal exactly matches thepart of the T₃R₁ signal which is trying to be removed or discounted, andT₂R₁ can be subtracted from T₃R₁. This produces the (T₃R₁−T₂R₁) part ofthe x₃ equation above.

The x₃ equation above also has a scaling factor of ½. This is tonormalize x₃ to match the x₁ which only has a contribution from a singletransmitter receiver pair. To put it another way, without the scalingfactor, the x₁ and x₃ calculations would have different dynamic ranges.Conceptually, two one-gap signals are being added together in the x₃equation, where (T₂R₂−T₃R₂) comprises one of the one-gap signals and(T₃R₁−T₂R₁) comprises the other one-gap signal. In contrast, the x₁equation only has a contribution from one one-gap signal.

This logic may be used to construct the x₂ and x₄ equations above. Forthe x₂ gap, the two signals which pass through that gap are the T₂R₁signal and the T₃R₁. The former signal is a one-gap signal and thereforemay be used as-is. However, the T₃R₁ signal is a two-gap signal and partof it must be subtracted out. The T₂R₂ signal is close, but it is notperfect because it is itself a two-gap signal. However, if the T₃R₂signal is subtracted from T₂R₂, then that difference (i.e., T₂R₂−T₃R₂)may be subtracted from T₃R₁. This produces the T₃R₁−(T₂R₂−T₃R₂) part ofthe x₂ equation. For the reasons described above, the x₂ equationincludes a ½ scaling factor. The x₄ equation can be constructed in asimilar manner.

With an amplitude metric calculated for each gap as described above(e.g., x₁, x₂, x₃, etc.), a discrete signal is constructed which is usedto both identify touches and output a force value for each identifiedtouch. The following figure illustrates an example of such a signal.

FIG. 24 is a diagram illustrating two embodiments of a discrete signalconstructed using amplitude metrics. In the example shown, diagram 2400shows a discrete signal generated for the example of FIG. 21. Theamplitude metric for each gap is plotted in this diagram, so that thex-axis corresponds to a particular gap location and the y-axiscorresponds to the value or amplitude metric calculated for thatparticular gap, as described above.

A threshold (2402) is used to identify any touches. In this example, theonly gap location which has an amplitude metric greater than threshold2402 is the x₃ gap. As such, a single touch at the x₃ gap is identified.The force value which is output for this identified touch is theamplitude metric calculated for x₃. In some embodiments, if gaps aresufficiently small compared to the size of the touch objects (e.g., afinger), the location of the touch may be interpolated on a sub-gapscale by weighting the location of each gap by its amplitude metric.

Diagram 2450 shows another scenario where two touches are identified. Asdescribed above, the amplitude metrics for the gaps between transmittersand/or receivers are calculated and plotted. In this example, twotouches are identified: a first touch (2452) at the x₂, x₃, and x₄ gapsand a second touch (2454) at the x₈ and x₉ gaps. In this example, thelargest amplitude metric for each touch is output as the force value forthat touch. This means outputting the value calculated for x₃ as theforce value for the first touch and outputting the value for x₉ as theforce value for the second touch. In some embodiments, the sum of thevalues above the threshold is output as the force of the touch.

The following figures describe these processes of generating amplitudemetrics and comparing the amplitude metrics against a threshold moreformally in flowcharts.

FIG. 25 is a flowchart illustrating an embodiment of a process toidentify a touch input using a first amplitude metric associated withthe part of the first region that is not part of the second region. Insome embodiments, the process of FIG. 25 is used at step 1674 in FIG.16. It is noted that the receiver referred to in FIG. 16 is referred toin this process as a second receiver.

At 2500, a first amplitude metric associated with the part of the firstregion that is not part of the second region is generated based at leastin part on: (1) a first amplitude associated with the first propagatingsignal from the first transmitter to the second receiver, (2) a secondamplitude associated with the second propagating signal from the secondtransmitter to the second receiver, (3) a third amplitude associatedwith a third propagating signal from the second transmitter to a firstreceiver, and (4) a fourth amplitude associated with a fourthpropagating signal from the first transmitter to the first receiver. Inone example of step 2500, x₃=½((T₂R₂−T₃R₂)+(T₃−T₂R₁)). It is noted thatthe indexes of the transmitters recited in this flowchart do not matchthe indexes of the transmitters in the x₁ equations above, nor theindexes of the transmitters in FIG. 21.

At 2502, the first amplitude metric is compared against a threshold. At2504, in the event the first amplitude metric exceeds the threshold: (1)the part of the first region that is not part of the second region isincluded in the touch input and (2) in the event the first amplitudemetric is a largest amplitude metric associated with the touch input,the first amplitude metric is output as a force value associated withthe touch input. See, for example, diagram 2400 in FIG. 24 It is notedthat an identified touch input may span or include more than one gap,and other gaps may be included in the identified touch input.

FIG. 26 is a flowchart illustrating an embodiment of a process togenerate a first amplitude metric associated with a part of a firstregion that is not part of a second region. In some embodiments, theprocess of FIG. 26 is used at step 2500 in FIG. 25.

At 2600, the amplitude associated with the first propagating signal fromthe first transmitter to the second receiver is added. See, for example,the first term from the x₃ equation above where T₂R₂ is added (thetransmitter/receiver numbering in the x₃ equation does not necessarilymatch those recited by FIG. 26).

At 2602, the amplitude associated with the second propagating signalfrom the second transmitter to the second receiver is subtracted. See,for example, the second term from the x₃ equation above where T₃R₂ issubtracted (the transmitter/receiver numbering in the x₃ equation doesnot necessarily match those recited by FIG. 26).

At 2604, the amplitude associated with the third propagating signal fromthe second transmitter to a first receiver is added. See, for example,the third term from the x₃ equation above where T₃R₁ is added (thetransmitter/receiver numbering in the x₃ equation does not necessarilymatch those recited by FIG. 26).

At 2606, the amplitude associated with the fourth propagating signalfrom the first transmitter to the first receiver is subtracted. See, forexample, the fourth term from the x₃ equation above where T₂R₁ issubtracted (the transmitter/receiver numbering in the x₃ equation doesnot necessarily match those recited by FIG. 26).

In some embodiments, a scaling factor is applied to the inputs or termsadded/subtracted above. In some other embodiments, the amplitude metricassociated with a different gap location is adjusted (e.g., theamplitude metric associated with x₁ is multiplied by 2).

FIG. 27 is a flowchart illustrating an embodiment of a process toidentify a touch input using a second amplitude metric associated withthe second region. In some embodiments, this process is performed inaddition to the process of FIG. 16.

At 2700, a second amplitude metric associated with the second region isgenerated based at least in part on: (1) a first amplitude associatedwith the first propagating signal from the first transmitter to thesecond receiver, (2) a second amplitude associated with the secondpropagating signal from the second transmitter to the second receiver,(3) a third amplitude associated with a third propagating signal fromthe second transmitter to a first receiver, and (4) a fourth amplitudeassociated with a fourth propagating signal from the first transmitterto the first receiver. See, for example, the x₄ equation describedabove.

At 2702, the second amplitude metric is compared against a threshold. At2704, in the event the second amplitude metric exceeds the threshold:(1) the second region is included in the touch input and (2) in theevent the second amplitude metric is a largest amplitude metricassociated with the touch input, the second amplitude metric is outputas a force value associated with the touch input. See, for example,identified touch 2452 in FIG. 24. In that example, the amplitude metriccalculated for x₄ is not the largest in identified touch 2452, so itwould not be output as the force value for that identified touch.

FIG. 28 is a flowchart illustrating an embodiment of a process togenerate a second amplitude metric associated with a second region. Insome embodiments, step 2700 in FIG. 27 includes the process of FIG. 28.As described above, a scaling factor may be applied to this amplitudemetric or some other amplitude metric may be scaled (e.g., the amplitudemetric for x₁).

At 2800, the amplitude associated with the second propagating signalfrom the second transmitter to the second receiver is added. See, forexample, the first term in the x₄ equation above where T₃R₂ is added(the transmitter/receiver numbering in the x₃ equation do notnecessarily match those recited by FIG. 28).

At 2802, the amplitude associated with the first propagating signal fromthe first transmitter to the second receiver is added. See, for example,the second term in the x₄ equation above where T₂R₂ is added (thetransmitter/receiver numbering in the x₃ equation do not necessarilymatch those recited by FIG. 28).

At 2804, the amplitude associated with the third propagating signal fromthe second transmitter to a first receiver is subtracted. See, forexample, the third term in the x₄ equation above where T₃R₁ issubtracted (the transmitter/receiver numbering in the x₃ equation do notnecessarily match those recited by FIG. 28).

At 2806, the amplitude associated with the fourth propagating signalfrom the first transmitter to the first receiver is added. See, forexample, the fourth term in the x₄ equation above where T₂R₁. is added(the transmitter/receiver numbering in the x₃ equation do notnecessarily match those recited by FIG. 28).

FIG. 29 is a block diagram illustrating an embodiment of a touch andforce sensor. For brevity and readability, some components, such as ananalog-to-digital converter and transformers to change the signal fromtime-domain to frequency-domain (or vice versa), are not shown here.Among other things, these exemplary components show some of thepre-processing performed before the amplitude of a signal is used todetect a touch and/or estimate an amount of force. In some embodiments,the exemplary blocks shown are implemented on a touch and force sensorand/or on a processor (e.g., an FPGA, an ASIC, or a general purposeprocessor).

Band pass filter 2900 is used to filter out information outside of someband pass range. For example, the transmitter may transmit informationin some pre-defined range of (e.g., carrier and/or code) frequencies. Atthe receiver, any signal outside of this range is filtered out in orderto reduce the amount of noise or error.

Next, decoding (2902) is performed. As described above, time-shiftedversions of the same PRBS are used by the different transmitter indexes(e.g., T₁, T₂, etc.) to create orthogonality between the differenttransmitters and/or transmitted signals. Decoding in this exampleincludes performing a correction with the transmitted signal. In FIG.21, if the signal received by the second receiver (2108) is decoded,performing a correlation will produce four distinct peaks: onecorresponding to the second transmitter (2120), another corresponding tothe third transmitter (2118), and so on.

With ultrasonic signals, different frequencies travel through the mediumat different speeds. So, at the receiver, higher frequencies arrivebefore slower frequencies, which results in a “smeared” signal at thereceiver. The dispersion compensator (2904) compensates for this sohigher frequencies and lower frequencies which left the transmitter atthe same time but arrived at different times are aligned again aftercompensation.

The peaks (e.g., after decoding and dispersion compensation) areexpected to have a certain curved shape. Matched filter 2906 filters outparts of the peaks outside of this ideal curved shape, again to reducenoise or errors.

Peak locator 2908 finds the location of the peaks in the signal. Forexample, if there are four known peaks, then the locations or offsets ofthe peaks in the signals may be identified. The locations or offsets ofthe peaks are then passed to amplitude metric generator (2910), whichtakes the absolute value of the signal at those locations or offsets andthen uses the absolute values to generate an amplitude metric for eachgap (e.g., x₁, x₂, x₃, etc.) as described above. As described above,amplitude metric generator 2910 inputs the appropriate amplitudereferences from reference storage 2912 in order to generate theamplitude metrics. The amplitude references stored in reference storage2912 may be updated as appropriate.

The amplitude metrics (e.g., x₁, x₂, x₃, etc.) are passed from amplitudemetric generator 2910 to reference comparator 2914. Reference comparatorcompares the amplitude metrics against a threshold (see, e.g., FIG. 24)and identifies touches when/where the amplitude metric(s) exceed thethreshold. The threshold used in the comparison is stored in referencestorage 2912 and may be updated as appropriate. The identified touchesand corresponding force values are output by reference comparator 2914.

Although the foregoing embodiments have been described in some detailfor purposes of clarity of understanding, the invention is not limitedto the details provided. There are many alternative ways of implementingthe invention. The disclosed embodiments are illustrative and notrestrictive.

What is claimed is:
 1. A sensor, comprising: a plurality ofpiezoresistive elements fabricated on a first side of a semiconductorsubstrate, wherein the semiconductor substrate has a thickness that isless than 300 microns, and a second side of the semiconductor substrateis configured to be coupled to an object where a physical disturbance isto be detected; and a plurality of electrical connection terminalscoupled to the first side of the semiconductor substrate that isopposite the second side of the semiconductor substrate, wherein thesecond side is configured to face towards an internal sidewall of ahousing of an electronic device where the physical disturbance is to bedetected; wherein at least a first portion of the plurality ofelectrical connection terminals is configured to be connected to asignal transmitter and receive from the signal transmitter an encodedsignal that has been generated by modulating a carrier signal using abinary sequence; wherein at least a second portion of the plurality ofelectrical connection terminals is configured to be connected to asignal receiver and provide an output version of the encoded signalencoding the binary sequence for correlation in detecting the physicaldisturbance; and wherein the plurality of piezoresistive elements havebeen fabricated on the first side of the semiconductor substratetogether as a single chip configured to allow the semiconductorsubstrate to physically bend to detect the physical disturbance, andwherein the single chip is configured to be coupled to the internalsidewall of the housing of the electronic device along with a pluralityof other instances of other chips that each include a different set ofpiezoresistive elements to detect the physical disturbance on thehousing of the electronic device, and wherein the single chip andanother chip included in the plurality of other instances of other chipsare connected to different signal transmitters providing differentencoded signals via different independent electrical connections but areconnected to the same signal receiver via a shared electricalconnection.
 2. The sensor of claim 1, wherein the plurality ofpiezoresistive elements includes a resistor.
 3. The sensor of claim 1,wherein the plurality of piezoresistive elements includes a transistor.4. The sensor of claim 1, wherein the substrate is a monocrystallinesilicon substrate.
 5. The sensor of claim 1, wherein the physicaldisturbance is a strain.
 6. The sensor of claim 1, wherein the pluralityof piezoresistive elements includes four piezoresistive elements thatare connected together in two parallel paths of two piezoresistiveelements in series.
 7. The sensor of claim 1, wherein the plurality ofpiezoresistive elements include microelectromechanical elements.
 8. Thesensor of claim 1, wherein the thickness of the substrate is thinner ascompared to an original thickness of a semiconductor wafer that includedthe plurality of piezoresistive elements of the semiconductor substrate.9. The sensor of claim 1, wherein the plurality of electrical connectionterminals are coupled to preformed solder balls.
 10. The sensor of claim1, wherein the electrical connection terminals are arranged on thesensor in a symmetrical configuration.
 11. The sensor of claim 1,wherein a same one of the electrical connection terminals can be eitherused as a signal input electrical connection terminal or a signal outputelectrical connection terminal.
 12. A device, comprising: a plurality ofpiezoresistive elements fabricated on a first side of a semiconductorsubstrate, wherein a second side of the semiconductor substrate isconfigured to be coupled to an object wherein a physical disturbance isto be detected, and the semiconductor substrate has a reduced thicknessthat is less than 300 microns to allow bending of the semiconductorsubstrate to detect the physical disturbance; and a plurality ofelectrical connection terminals coupled to the first side of thesemiconductor substrate that is opposite the second side of thesemiconductor substrate, wherein the second side is configured to facetowards an internal sidewall of a housing of an electronic device wherethe physical disturbance is to be detected; wherein at least a firstportion of the plurality of electrical connection terminals isconfigured to be connected to a signal transmitter and receive from thesignal transmitter an encoded signal that has been generated bymodulating a carrier signal using a binary sequence; wherein at least asecond portion of the plurality of electrical connection terminals isconfigured to be connected to a signal receiver and provide an outputversion of the encoded signal encoding the binary sequence forcorrelation in detecting the physical disturbance; and wherein theplurality of piezoresistive elements have been fabricated on the firstside of the semiconductor substrate together as a single chip, andwherein the single chip is configured to be coupled to the internalsidewall of the housing of the electronic device along with a pluralityof other instances of other chips that each include a different set ofpiezoresistive elements to detect the physical disturbance on thehousing of the electronic device, and wherein the single chip andanother chip included in the plurality of other instances of other chipsare connected to different signal transmitters providing differentencoded signals via different independent electrical connections but areconnected to the same signal receiver via a shared electricalconnection.
 13. The device of claim 12, wherein the plurality ofpiezoresistive elements includes a resistor.
 14. The device of claim 12,wherein the plurality of piezoresistive elements includes a transistor.15. The device of claim 12, wherein the substrate is a monocrystallinesilicon substrate.
 16. The device of claim 12, wherein the plurality ofpiezoresistive elements includes four piezoresistive elements that areconnected together in two parallel paths of two piezoresistive elementsin series.
 17. The device of claim 12, wherein the plurality ofelectrical connection terminals are coupled to preformed solder balls.18. The device of claim 12, wherein the electrical connection terminalsare arranged on the sensor in a symmetrical configuration.
 19. Thedevice of claim 12, wherein a same one of the electrical connectionterminals can be either used as a signal input electrical connectionterminal or a signal output electrical connection terminal.
 20. Adevice, comprising: a plurality of piezoresistive elements fabricated ona first side of a semiconductor substrate, wherein a second side of thesemiconductor substrate is configured to be coupled to an object where aphysical disturbance is to be detected; and a plurality of electricalconnection terminals coupled to the first side of the semiconductorsubstrate that is opposite the second side of the semiconductorsubstrate, wherein the second side is configured to face towards aninternal sidewall of a housing of an electronic device where thephysical disturbance is to be detected; wherein at least a first portionof the plurality of electrical connection terminals is configured to beconnected to a signal transmitter and receive from the signaltransmitter an encoded signal that has been generated by modulating acarrier signal using a binary sequence; wherein at least a secondportion of the plurality of electrical connection terminals isconfigured to be connected to a signal receiver and provide an outputversion of the encoded signal encoding the binary sequence forcorrelation in detecting the physical disturbance; and wherein theplurality of piezoresistive elements have been fabricated on the firstside of the semiconductor substrate together as a single chip configuredto allow the semiconductor substrate to physically bend to detect thephysical disturbance, and wherein the single chip is configured to becoupled to the internal sidewall of the housing of the electronic devicealong with a plurality of other instances of other chips that eachinclude a different set of piezoresistive elements to detect thephysical disturbance on the housing of the electronic device, andwherein the single chip and another chip included in the plurality ofother instances of other chips are connected to different signaltransmitters providing different encoded signals via differentindependent electrical connections but are connected to the same signalreceiver via a shared electrical connection.